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SQLite.jl Documentation

High-level interface

DBInterface.execute(::SQLite.Stmt, ::DBInterface.StatementParams)
SQLite.load!

Types/Functions

SQLite.DB
SQLite.Stmt
SQLite.bind!
SQLite.createtable!
SQLite.drop!
SQLite.dropindex!
SQLite.createindex!
SQLite.removeduplicates!
SQLite.tables
SQLite.columns
SQLite.indices
SQLite.enable_load_extension
SQLite.register
SQLite.@register
SQLite.@sr_str
SQLite.sqlreturn
SQLite.transaction
SQLite.commit
SQLite.rollback
SQLite.backup

User Defined Functions

[SQLite Regular Expressions](@id regex)

SQLite provides syntax for calling the regexp function from inside WHERE clauses. Unfortunately, however, sqlite does not provide a default implementation of the regexp function. It can be easily added, however, by calling SQLite.@register db SQLite.regexp

The function can be called in the following ways (examples using the Chinook Database)

julia> using SQLite

julia> db = SQLite.DB("Chinook_Sqlite.sqlite")

julia> # using SQLite's in-built syntax

julia> DBInterface.execute(db, "SELECT FirstName, LastName FROM Employee WHERE LastName REGEXP 'e(?=a)'") |> DataFrame
1x2 ResultSet
| Row | "FirstName" | "LastName" |
|-----|-------------|------------|
| 1   | "Jane"      | "Peacock"  |

julia> # explicitly calling the regexp() function

julia> DBInterface.execute(db, "SELECT * FROM Genre WHERE regexp('e[trs]', Name)") |> DataFrame
6x2 ResultSet
| Row | "GenreId" | "Name"               |
|-----|-----------|----------------------|
| 1   | 3         | "Metal"              |
| 2   | 4         | "Alternative & Punk" |
| 3   | 6         | "Blues"              |
| 4   | 13        | "Heavy Metal"        |
| 5   | 23        | "Alternative"        |
| 6   | 25        | "Opera"              |

julia> # you can even do strange things like this if you really want

julia> DBInterface.execute(db, "SELECT * FROM Genre ORDER BY GenreId LIMIT 2") |> DataFrame
2x2 ResultSet
| Row | "GenreId" | "Name" |
|-----|-----------|--------|
| 1   | 1         | "Rock" |
| 2   | 2         | "Jazz" |

julia> DBInterface.execute(db, "INSERT INTO Genre VALUES (regexp('^word', 'this is a string'), 'My Genre')") |> DataFrame
1x1 ResultSet
| Row | "Rows Affected" |
|-----|-----------------|
| 1   | 0               |

julia> DBInterface.execute(db, "SELECT * FROM Genre ORDER BY GenreId LIMIT 2") |> DataFrame
2x2 ResultSet
| Row | "GenreId" | "Name"     |
|-----|-----------|------------|
| 1   | 0         | "My Genre" |
| 2   | 1         | "Rock"     |

Due to the heavy use of escape characters, you may run into problems where julia parses out some backslashes in your query, for example "\y" simply becomes "y". For example, the following two queries are identical:

julia> DBInterface.execute(db, "SELECT * FROM MediaType WHERE Name REGEXP '-\d'") |> DataFrame
1x1 ResultSet
| Row | "Rows Affected" |
|-----|-----------------|
| 1   | 0               |

julia> DBInterface.execute(db, "SELECT * FROM MediaType WHERE Name REGEXP '-d'") |> DataFrame
1x1 ResultSet
| Row | "Rows Affected" |
|-----|-----------------|
| 1   | 0               |

This can be avoided in two ways. You can either escape each backslash yourself or you can use the raw"..." string literal. The previous query can then successfully be run like so:

julia> # manually escaping backslashes

julia> DBInterface.execute(db, "SELECT * FROM MediaType WHERE Name REGEXP '-\\d'") |> DataFrame
1x2 ResultSet
| Row | "MediaTypeId" | "Name"                        |
|-----|---------------|-------------------------------|
| 1   | 3             | "Protected MPEG-4 video file" |


julia> DBInterface.execute(db, raw"SELECT * FROM MediaType WHERE Name REGEXP '-\d'") |> DataFrame
1x2 ResultSet
| Row | "MediaTypeId" | "Name"                        |
|-----|---------------|-------------------------------|
| 1   | 3             | "Protected MPEG-4 video file" |

Custom Scalar Functions

SQLite.jl also provides a way that you can implement your own Scalar Functions. This is done using the SQLite.register function and macro.

SQLite.@register takes a SQLite.DB and a function. The function can be in block syntax:

julia> SQLite.@register db function add3(x)
       x + 3
       end

inline function syntax:

julia> SQLite.@register db mult3(x) = 3 * x

and previously defined functions:

julia> SQLite.@register db sin

The SQLite.register function takes optional arguments; nargs which defaults to -1, name which defaults to the name of the function, isdeterm which defaults to true. In practice these rarely need to be used.

The SQLite.register function uses the SQLite.sqlreturn function to return your function's return value to SQLite. By default, sqlreturn maps the returned value to a native SQLite type or, failing that, serializes the julia value and stores it as a BLOB. To change this behaviour simply define a new method for sqlreturn which then calls a previously defined method for sqlreturn. Methods which map to native SQLite types are

sqlreturn(context, ::NullType)
sqlreturn(context, val::Int32)
sqlreturn(context, val::Int64)
sqlreturn(context, val::Float64)
sqlreturn(context, val::UTF16String)
sqlreturn(context, val::String)
sqlreturn(context, val::Any)

As an example, say you would like BigInts to be stored as TEXT rather than a BLOB. You would simply need to define the following method:

sqlreturn(context, val::BigInt) = sqlreturn(context, string(val))

Another example is the SQLite.sqlreturn used by the regexp function. For regexp to work correctly, it must return it must return an Int (more specifically a 0 or 1) but occursin (used by regexp) returns a Bool. For this reason the following method was defined:

sqlreturn(context, val::Bool) = sqlreturn(context, int(val))

Any new method defined for sqlreturn must take two arguments and must pass the first argument straight through as the first argument.

Custom Aggregate Functions

Using the SQLite.register function, you can also define your own aggregate functions with largely the same semantics.

The SQLite.register function for aggregates must take a SQLite.DB, an initial value, a step function and a final function. The first argument to the step function will be the return value of the previous function (or the initial value if it is the first iteration). The final function must take a single argument which will be the return value of the last step function.

julia> dsum(prev, cur) = prev + cur

julia> dsum(prev) = 2 * prev

julia> SQLite.register(db, 0, dsum, dsum)

If no name is given, the name of the first (step) function is used (in this case "dsum"). You can also use lambdas; the following does the same as the previous code snippet

julia> SQLite.register(db, 0, (p,c) -> p+c, p -> 2p, name="dsum")

Saving an in-memory database to a file

An in-memory database (SQLite.DB() with no path) lives only for the lifetime of the connection. To persist it, use SQLite.backup, which copies the database to path via the SQLite backup API:

julia> db = SQLite.DB();  # in-memory database

julia> DBInterface.execute(db, "CREATE TABLE t (id INTEGER, name TEXT)");

julia> DBInterface.execute(db, "INSERT INTO t VALUES (1, 'alice'), (2, 'bob')");

julia> SQLite.backup(db, "snapshot.sqlite")
"snapshot.sqlite"

The file can then be reopened as an ordinary on-disk database:

julia> db2 = SQLite.DB("snapshot.sqlite");

julia> DBInterface.execute(db2, "SELECT * FROM t") |> DataFrame
2×2 DataFrame
 Row │ id     name
     │ Int64  String
─────┼───────────────
   1 │     1  alice
   2 │     2  bob

The same call works for any open SQLite.DB, not just in-memory ones — for example, snapshotting an on-disk database to a separate file.