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Initial implementation of CURSORs.
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‎CLAUDE.md‎

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@@ -127,6 +127,9 @@ Three entry points share one per-connection undo log: implicit (statement-level
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- `INSERT ... OUTPUT INSERTED.<col>` (single-row).
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- `MERGE INTO target USING <source> ON … WHEN [NOT] MATCHED [BY TARGET|SOURCE] [AND …] THEN UPDATE|DELETE|INSERT … [OUTPUT $action, …]` — source = VALUES / SELECT / set-op / bare-table; multiple per-family AND-conditioned clauses; trailing `;` required. Msg 5324 / 8672 / 10713 / 10714 enforced. Triggers fire one INSERT → UPDATE → DELETE pass with combined affected rows. See [`docs/claude/dml.md`](docs/claude/dml.md).
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### Cursors
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Session-scoped T-SQL cursors: `DECLARE <name> [INSENSITIVE][SCROLL] CURSOR [LOCAL|GLOBAL][FORWARD_ONLY|SCROLL][STATIC|KEYSET|DYNAMIC|FAST_FORWARD][READ_ONLY|…] FOR <select> [FOR {READ ONLY|UPDATE [OF cols]}]`, `OPEN`, `FETCH NEXT|PRIOR|FIRST|LAST|ABSOLUTE n|RELATIVE n [FROM] <cursor> [INTO @v,…]`, `CLOSE`, `DEALLOCATE`, plus `@@FETCH_STATUS` / `@@CURSOR_ROWS` / `CURSOR_STATUS` and positioned `WHERE CURRENT OF` UPDATE/DELETE. Effective sensitivity resolves at DECLARE: non-updatable query (not a single base table with a PK/UNIQUE) → STATIC; STATIC frozen-snapshot, KEYSET frozen-membership with live value re-reads (deleted member → `@@FETCH_STATUS=-2`), DYNAMIC fully live (skips deletes, sees inserts, `@@CURSOR_ROWS=-1`). Position tracked by the logical unique key (not a RID — UPDATE relocates rows). Errors Msg 16905/16915/16916/16917/16924/16925/16929/16931 probe-confirmed verbatim. Cursor variables (`DECLARE @c CURSOR`) raise `NotSupportedException`. See [`docs/claude/cursors.md`](docs/claude/cursors.md).
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### EF Core adapter coverage
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`UseSqlServerSimulator(...)` covers seven SqlParameter-downcast pairs: `DateOnly→date`, `DateTime→date`, `DateTime→smalldatetime`, `TimeOnly→time(N)`, `TimeSpan→time(N)`, `decimal→money`, `decimal→smallmoney`. Without the adapter those mappings throw at SaveChanges. MAX-string family flows through plain `UseSqlServer`.
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@@ -146,6 +149,7 @@ Per-feature deep-dives live under `docs/claude/`. Each entry below is a trigger:
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- **`Selection`, aggregates, window functions, set ops, CASE, OFFSET/FETCH** → [`query.md`](docs/claude/query.md).
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- **UPDATE / DELETE / INSERT…SELECT / SELECT…INTO / rowversion (incl. `@@DBTS` / `MIN_ACTIVE_ROWVERSION`) / identity helpers (`@@IDENTITY` / `SCOPE_IDENTITY` / `IDENT_CURRENT` / `IDENT_INCR` / `IDENT_SEED`) / `@@ROWCOUNT` / `ROWCOUNT_BIG` / OUTPUT / MERGE** → [`dml.md`](docs/claude/dml.md).
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- **Variables, control flow (IF/WHILE/BREAK/CONTINUE/RETURN), TRY/CATCH+THROW+ERROR_*, `@@ERROR` / `@@TRANCOUNT` / `XACT_STATE`, PRINT, WAITFOR** → [`control-flow.md`](docs/claude/control-flow.md).
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- **Cursors (`DECLARE … CURSOR` / `OPEN` / `FETCH` / `CLOSE` / `DEALLOCATE`, STATIC / KEYSET / DYNAMIC sensitivity, scroll fetches, `@@FETCH_STATUS` / `@@CURSOR_ROWS` / `CURSOR_STATUS`, `WHERE CURRENT OF`)** → [`cursors.md`](docs/claude/cursors.md).
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- **CTE shapes / recursive-CTE error handling** → [`ctes.md`](docs/claude/ctes.md).
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- **JSON_VALUE / JSON_QUERY / JSON_MODIFY / JSON_OBJECT / JSON_ARRAY / JSON_PATH_EXISTS / ISJSON / OPENJSON** → [`json.md`](docs/claude/json.md).
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- **Name resolution, schema lookup, CREATE / DROP / ALTER SCHEMA TRANSFER, `OBJECT_ID` / `OBJECT_NAME` / `OBJECT_SCHEMA_NAME` / `SCHEMA_ID` / `SCHEMA_NAME` / `DB_ID` / `DB_NAME`, cross-DB read routing** → [`schemas.md`](docs/claude/schemas.md).
@@ -225,3 +229,4 @@ Per-feature deep-dives live under `docs/claude/`. Each entry below is a trigger:
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- **`STRING_SPLIT(..., ..., cast(@v as int))` — wrapped variable accepted**: the simulator's `enable_ordinal` const-only gate rejects bare `@v` (Msg 8748, matching real) but a Cast / Parenthesized wrapper around the variable slips past the gate. Real SQL Server rejects all variable-bearing shapes regardless of wrapping. No real-world emission hits this — the const-only restriction means `@v` ergonomics are weak in any form.
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- **`OPENJSON` `WITH ... AS JSON`** on `nvarchar(max)` raises `NotSupportedException` even though real SQL Server accepts the column form there (sub-tree extraction not modeled). Non-`nvarchar(max)` columns with `AS JSON` raise **Msg 13618**, matching real.
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- **`FOR SYSTEM_TIME` qualified-name format**: real SQL Server pads temp-table names in Msg 13544 with their internal allocation suffix (`#x____...___…000000000148`); the simulator emits the bare `tempdb.dbo.#x` form. Same Msg number / framing, less verbose name.
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- **Cursor edges**: `@@CURSOR_ROWS` is `-1` throughout for DYNAMIC (real SQL Server may report a transient positive count pre-fetch); a keyset `-2` (deleted-member) fetch leaves the `INTO` variables unchanged rather than zeroing/NULLing them; `FETCH` without `INTO` omits the trailing `ROWSTAT` column real SQL Server appends. See [`docs/claude/cursors.md`](docs/claude/cursors.md).

‎SqlServerSimulator.Tests/CursorTests.cs‎

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using static Microsoft.VisualStudio.TestTools.UnitTesting.Assert;
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using static SqlServerSimulator.TestHelpers;
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namespace SqlServerSimulator;
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/// <summary>
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/// T-SQL cursors: DECLARE … CURSOR / OPEN / FETCH / CLOSE / DEALLOCATE,
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/// the STATIC / KEYSET / DYNAMIC sensitivity model, scroll fetches,
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/// <c>@@FETCH_STATUS</c> / <c>@@CURSOR_ROWS</c> / <c>CURSOR_STATUS</c>, and
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/// positioned <c>WHERE CURRENT OF</c> DML. Behavior probed against SQL Server
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/// 2025. A cursor is session-scoped, so each lifecycle runs as one batch
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/// string on a single connection.
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/// </summary>
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[TestClass]
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public sealed class CursorTests
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{
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private const string Seed =
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"create table t (id int primary key, name varchar(20)); " +
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"insert t values (1,'a'),(2,'b'),(3,'c');";
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[TestMethod]
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public void ForwardLoop_AccumulatesAllRowsInOrder()
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=> AreEqual("1:a;2:b;3:c;", new Simulation().ExecuteScalar(Seed + """
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declare @id int, @name varchar(20), @log varchar(200) = '';
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declare c cursor for select id, name from t order by id;
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open c;
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fetch next from c into @id, @name;
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while @@fetch_status = 0
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begin
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set @log = @log + convert(varchar, @id) + ':' + @name + ';';
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fetch next from c into @id, @name;
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end
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close c; deallocate c;
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select @log
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"""));
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[TestMethod]
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public void FetchPastEnd_FetchStatusIsMinusOne()
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=> AreEqual(-1, ExecuteScalar<int>(Seed + """
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declare @id int, @name varchar(20);
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declare c cursor for select id, name from t;
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open c;
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while @@fetch_status = 0 fetch next from c into @id, @name;
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select @@fetch_status
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"""));
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[TestMethod]
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public void FetchPastEnd_VariablesRetainLastFetchedValue()
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=> AreEqual(3, ExecuteScalar<int>(Seed + """
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declare @id int, @name varchar(20);
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declare c cursor for select id, name from t order by id;
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open c;
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while @@fetch_status = 0 fetch next from c into @id, @name;
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select @id
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"""));
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[TestMethod]
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public void CursorRows_Static_ReturnsRowCount()
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=> AreEqual(3, ExecuteScalar<int>(Seed + """
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declare c cursor static for select id from t;
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open c;
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select @@cursor_rows
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"""));
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[TestMethod]
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public void CursorRows_Dynamic_ReturnsMinusOne()
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=> AreEqual(-1, ExecuteScalar<int>(Seed + """
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declare c cursor dynamic for select id from t;
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open c;
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select @@cursor_rows
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"""));
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[TestMethod]
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public void OpenUndeclaredCursor_RaisesMsg16916()
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=> new Simulation().AssertSqlError("open nope", 16916,
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"A cursor with the name 'nope' does not exist.");
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[TestMethod]
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public void DuplicateDeclare_RaisesMsg16915()
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=> new Simulation().AssertSqlError(Seed + """
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declare dup cursor for select id from t;
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declare dup cursor for select id from t;
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""", 16915, "A cursor with the name 'dup' already exists.");
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[TestMethod]
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public void OpenAlreadyOpen_RaisesMsg16905()
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=> new Simulation().AssertSqlError(Seed + """
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declare c cursor for select id from t;
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open c; open c;
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""", 16905, "The cursor is already open.");
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[TestMethod]
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public void CloseNotOpen_RaisesMsg16917()
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=> new Simulation().AssertSqlError(Seed + """
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declare c cursor for select id from t;
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close c;
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""", 16917, "Cursor is not open.");
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[TestMethod]
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public void FetchNotOpen_RaisesMsg16917()
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=> new Simulation().AssertSqlError(Seed + """
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declare @v int;
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declare c cursor for select id from t;
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fetch next from c into @v;
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""", 16917, "Cursor is not open.");
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[TestMethod]
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public void FetchIntoColumnCountMismatch_RaisesMsg16924()
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=> new Simulation().AssertSqlError(Seed + """
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declare @only int;
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declare c cursor for select id, name from t;
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open c;
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fetch next from c into @only;
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""", 16924, "Cursorfetch: The number of variables declared in the INTO list must match that of selected columns.");
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[TestMethod]
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public void DeallocateUndeclared_RaisesMsg16916()
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=> new Simulation().AssertSqlError("deallocate nope", 16916,
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"A cursor with the name 'nope' does not exist.");
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[TestMethod]
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public void ScrollFetch_AllDirections()
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=> AreEqual("3|1|2|1|3", ExecuteScalar(Seed + """
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declare @s int, @log varchar(50) = '';
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declare c cursor scroll for select id from t order by id;
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open c;
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fetch last from c into @s; set @log = convert(varchar,@s);
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fetch first from c into @s; set @log = @log + '|' + convert(varchar,@s);
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fetch absolute 2 from c into @s; set @log = @log + '|' + convert(varchar,@s);
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fetch prior from c into @s; set @log = @log + '|' + convert(varchar,@s);
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fetch relative 2 from c into @s; set @log = @log + '|' + convert(varchar,@s);
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close c; deallocate c;
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select @log
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"""));
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[TestMethod]
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public void ScrollFetchOnForwardOnlyCursor_RaisesMsg16925()
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=> new Simulation().AssertSqlError(Seed + """
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declare @v int;
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declare c cursor forward_only for select id from t;
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open c;
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fetch absolute 2 from c into @v;
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""", 16925, "The fetch type Absolute cannot be used with dynamic cursors.");
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[TestMethod]
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public void StaticCursor_ImmuneToColumnChangeMidLoop()
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=> AreEqual("a;b;c;", new Simulation().ExecuteScalar(Seed + """
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declare @id int, @name varchar(20), @log varchar(200) = '';
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declare c cursor static for select id, name from t order by id;
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open c;
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fetch next from c into @id, @name;
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update t set name = 'CHANGED' where id = 2;
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while @@fetch_status = 0
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begin
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set @log = @log + @name + ';';
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fetch next from c into @id, @name;
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end
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select @log
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"""));
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[TestMethod]
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public void DynamicCursor_SeesColumnChangeMidLoop()
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=> AreEqual("a;CHANGED;c;", new Simulation().ExecuteScalar(Seed + """
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declare @id int, @name varchar(20), @log varchar(200) = '';
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declare c cursor dynamic for select id, name from t order by id;
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open c;
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fetch next from c into @id, @name;
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update t set name = 'CHANGED' where id = 2;
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while @@fetch_status = 0
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begin
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set @log = @log + @name + ';';
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fetch next from c into @id, @name;
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end
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select @log
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"""));
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[TestMethod]
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public void DynamicCursor_SkipsRowDeletedAhead()
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=> AreEqual("1;3;", new Simulation().ExecuteScalar(Seed + """
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declare @id int, @name varchar(20), @log varchar(200) = '';
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declare c cursor dynamic for select id, name from t order by id;
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open c;
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fetch next from c into @id, @name;
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delete t where id = 2;
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while @@fetch_status = 0
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begin
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set @log = @log + convert(varchar,@id) + ';';
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fetch next from c into @id, @name;
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end
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select @log
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"""));
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[TestMethod]
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public void DynamicCursor_SeesRowInsertedAhead()
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=> AreEqual("1;2;3;9;", new Simulation().ExecuteScalar(Seed + """
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declare @id int, @name varchar(20), @log varchar(200) = '';
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declare c cursor dynamic for select id, name from t order by id;
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open c;
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fetch next from c into @id, @name;
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insert t values (9, 'i');
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while @@fetch_status = 0
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begin
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set @log = @log + convert(varchar,@id) + ';';
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fetch next from c into @id, @name;
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end
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select @log
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"""));
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[TestMethod]
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public void KeysetCursor_SeesColumnChangeButNotInsert()
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=> AreEqual("a;K2;c;", new Simulation().ExecuteScalar(Seed + """
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declare @id int, @name varchar(20), @log varchar(200) = '';
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declare c cursor keyset for select id, name from t order by id;
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open c;
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fetch next from c into @id, @name;
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update t set name = 'K2' where id = 2;
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insert t values (9, 'i');
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while @@fetch_status = 0
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begin
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set @log = @log + @name + ';';
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fetch next from c into @id, @name;
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end
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select @log
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"""));
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[TestMethod]
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public void KeysetCursor_DeletedMember_FetchStatusMinusTwo()
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=> AreEqual(-2, ExecuteScalar<int>(Seed + """
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declare @id int, @name varchar(20);
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declare c cursor keyset for select id, name from t order by id;
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open c;
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fetch next from c into @id, @name; -- id 1
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delete t where id = 2;
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fetch next from c into @id, @name; -- keyset member 2, now deleted
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select @@fetch_status
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"""));
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[TestMethod]
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public void CursorStatus_OpenReturnsOne()
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=> AreEqual((short)1, ExecuteScalar<short>(Seed + """
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declare c cursor for select id from t;
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open c;
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select cursor_status('local', 'c')
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"""));
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[TestMethod]
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public void CursorStatus_NonexistentReturnsMinusThree()
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=> AreEqual((short)-3, ExecuteScalar<short>("select cursor_status('local', 'ghost')"));
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[TestMethod]
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public void WhereCurrentOf_UpdatesPositionedRow()
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=> AreEqual("POS", new Simulation().ExecuteScalar(Seed + """
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declare @id int;
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declare c cursor for select id from t order by id;
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open c;
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fetch next from c into @id; -- on id 1
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fetch next from c into @id; -- on id 2
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update t set name = 'POS' where current of c;
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close c; deallocate c;
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select name from t where id = 2
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"""));
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[TestMethod]
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public void WhereCurrentOf_DeletesPositionedRow()
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=> AreEqual(0, ExecuteScalar<int>(Seed + """
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declare @id int;
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declare c cursor for select id from t order by id;
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open c;
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fetch next from c into @id; -- on id 1
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delete from t where current of c;
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close c; deallocate c;
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select count(*) from t where id = 1
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"""));
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[TestMethod]
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public void WhereCurrentOf_ReadOnlyStaticCursor_RaisesMsg16929()
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=> new Simulation().AssertSqlError(Seed + """
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declare @id int;
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declare c cursor static for select id from t order by id;
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open c;
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fetch next from c into @id;
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update t set name = 'x' where current of c;
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""", 16929, "The cursor is READ ONLY.");
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[TestMethod]
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public void WhereCurrentOf_BeforeAnyFetch_RaisesMsg16931()
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=> new Simulation().AssertSqlError(Seed + """
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declare c cursor for select id from t order by id;
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open c;
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update t set name = 'x' where current of c;
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""", 16931, "There are no rows in the current fetch buffer.");
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[TestMethod]
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public void DeallocateWhileOpen_IsAllowed()
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=> AreEqual((short)-3, ExecuteScalar<short>(Seed + """
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declare c cursor for select id from t;
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open c;
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deallocate c;
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select cursor_status('local', 'c')
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"""));
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[TestMethod]
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public void NonUpdatableQuery_ForcedToStaticEvenWhenDynamicRequested()
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=> AreEqual(1, ExecuteScalar<int>(Seed + """
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declare c cursor dynamic for select count(*) from t;
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open c;
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select @@cursor_rows
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"""));
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[TestMethod]
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public void CursorVariable_NotSupported()
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=> Throws<NotSupportedException>(() => ExecuteScalar("declare @c cursor"));
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[TestMethod]
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public void FetchWithoutInto_YieldsSingleRowResultSet()
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{
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var sim = new Simulation();
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_ = sim.ExecuteNonQuery("create table t (id int primary key, name varchar(20)); insert t values (1,'a'),(2,'b')");
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using var conn = sim.CreateOpenConnection();
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_ = conn.CreateCommand("declare c cursor for select id, name from t order by id; open c").ExecuteNonQuery();
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using var reader = conn.CreateCommand("fetch next from c").ExecuteReader();
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IsTrue(reader.Read());
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AreEqual(1, reader.GetInt32(0));
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AreEqual("a", reader.GetString(1));
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IsFalse(reader.Read());
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}
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}

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