Fix SampleRatio fraction formatting and aliased negative integers

1. SampleRatio: Convert decimal values like 0.1 to fractions like 1/10
   in EXPLAIN output, matching ClickHouse's format for SAMPLE clauses.
   Added floatToFraction() helper to find simple fraction representation.

2. Aliased negative integers: Always output aliased negative integer
   literals as "Literal Int64_-N" instead of "Function negate". The
   previous code only did this in subquery context, but ClickHouse
   always uses the literal format for aliased expressions.

Fixes 4 explain tests.

Author: claude

internal/explain/expressions.go

@@ -418,22 +418,20 @@ func explainAliasedExpr(sb *strings.Builder, n *ast.AliasedExpr, depth int) {
 		}
 	case *ast.UnaryExpr:
 		// Handle negated numeric literals - output as Literal instead of Function negate
-		// For integers, only do this in subquery context (ClickHouse behavior)
+		// For aliased expressions, ClickHouse always shows negated integers as Literal Int64_-N
 		// For floats (especially inf/nan), always do this
 		if e.Op == "-" {
 			if lit, ok := e.Operand.(*ast.Literal); ok {
 				switch lit.Type {
 				case ast.LiteralInteger:
-					// Only convert to literal in subquery context
-					if inSubqueryContext {
-						switch val := lit.Value.(type) {
-						case int64:
-							fmt.Fprintf(sb, "%sLiteral Int64_%d (alias %s)\n", indent, -val, escapeAlias(n.Alias))
-							return
-						case uint64:
-							fmt.Fprintf(sb, "%sLiteral Int64_-%d (alias %s)\n", indent, val, escapeAlias(n.Alias))
-							return
-						}
+					// Always convert to literal for aliased expressions
+					switch val := lit.Value.(type) {
+					case int64:
+						fmt.Fprintf(sb, "%sLiteral Int64_%d (alias %s)\n", indent, -val, escapeAlias(n.Alias))
+						return
+					case uint64:
+						fmt.Fprintf(sb, "%sLiteral Int64_-%d (alias %s)\n", indent, val, escapeAlias(n.Alias))
+						return
 					}
 				case ast.LiteralFloat:
 					// Always convert negated floats to literals (especially for -inf, -nan)

internal/explain/tables.go

@@ -78,11 +78,53 @@ func formatSampleRatio(sb *strings.Builder, expr ast.Expression) {
 		formatSampleRatioOperand(sb, binExpr.Left)
 		sb.WriteString(" / ")
 		formatSampleRatioOperand(sb, binExpr.Right)
+	} else if lit, ok := expr.(*ast.Literal); ok && lit.Type == ast.LiteralFloat {
+		// Convert float to fraction if it's a simple ratio
+		if v, ok := lit.Value.(float64); ok {
+			num, den := floatToFraction(v)
+			if den > 1 {
+				fmt.Fprintf(sb, "%d / %d", num, den)
+				return
+			}
+		}
+		formatSampleRatioOperand(sb, expr)
 	} else {
 		formatSampleRatioOperand(sb, expr)
 	}
 }
 
+// floatToFraction converts a float to a simple fraction (numerator, denominator).
+// Returns (num, 1) if no simple fraction representation is found.
+func floatToFraction(f float64) (int64, int64) {
+	// Handle common sample ratios
+	// Try denominators from 2 to 1000
+	for den := int64(2); den <= 1000; den++ {
+		num := int64(f * float64(den))
+		// Check if this gives us back the original value (within floating point tolerance)
+		if float64(num)/float64(den) == f {
+			// Find GCD to simplify the fraction
+			g := gcd(num, den)
+			return num / g, den / g
+		}
+	}
+	// No simple fraction found, return as integer if possible
+	if f == float64(int64(f)) {
+		return int64(f), 1
+	}
+	return 0, 1
+}
+
+// gcd calculates the greatest common divisor of two integers
+func gcd(a, b int64) int64 {
+	if a < 0 {
+		a = -a
+	}
+	for b != 0 {
+		a, b = b, a%b
+	}
+	return a
+}
+
 func formatSampleRatioOperand(sb *strings.Builder, expr ast.Expression) {
 	if lit, ok := expr.(*ast.Literal); ok {
 		switch v := lit.Value.(type) {

parser/testdata/00056_view/metadata.json

@@ -1 +1 @@
-{"explain_todo":{"stmt6":true}}
+{}

parser/testdata/00276_sample/metadata.json

@@ -1,6 +1,5 @@
 {
   "explain_todo": {
-    "stmt13": true,
     "stmt14": true,
     "stmt15": true,
     "stmt16": true,
@@ -15,7 +14,6 @@
     "stmt32": true,
     "stmt33": true,
     "stmt34": true,
-    "stmt39": true,
-    "stmt9": true
+    "stmt39": true
   }
 }

parser/testdata/00578_merge_table_sampling/metadata.json

@@ -1 +1,6 @@
-{"explain_todo":{"stmt10":true,"stmt5":true,"stmt8":true,"stmt9":true}}
+{
+  "explain_todo": {
+    "stmt8": true,
+    "stmt9": true
+  }
+}

parser/testdata/01430_modify_sample_by_zookeeper_long/metadata.json

@@ -1,16 +1,9 @@
 {
   "explain_todo": {
-    "stmt11": true,
     "stmt12": true,
-    "stmt13": true,
-    "stmt16": true,
     "stmt17": true,
     "stmt18": true,
-    "stmt19": true,
-    "stmt22": true,
     "stmt25": true,
-    "stmt6": true,
-    "stmt7": true,
-    "stmt8": true
+    "stmt7": true
   }
 }