fix: stop declaring a column type the storage will not match

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Column type detection no longer declares a type the storage will not match. `strconv.ParseFloat` accepts Go source syntax that SQLite's numeric affinity does not convert, so a digit-separating underscore (`1_000`) or a hexadecimal float (`0x1p4`) made the column `REAL` while every value in it was stored as text. A datetime alongside a number did the same: the numeric type won on confidence and the datetime was stored as text under it. Both are TEXT now, which is what the storage always was. A caller reading the schema to plan a numeric comparison had no way to detect the difference.
+
 ## [0.35.1] - 2026-08-06
 
 ### Fixed

types.go

@@ -659,10 +659,31 @@ func isFloat(value string) bool {
 		return false
 	}
 
+	// strconv.ParseFloat accepts Go source syntax: digit-separating underscores
+	// ("1_000") and hexadecimal floats ("0x1p4"). SQLite's numeric affinity
+	// converts neither, so calling them numeric declared a REAL column whose
+	// values it then stored as text, leaving the schema and typeof() disagreeing.
+	if hasGoOnlyNumericSyntax(value) {
+		return false
+	}
+
 	_, err := strconv.ParseFloat(value, 64)
 	return err == nil
 }
 
+// hasGoOnlyNumericSyntax reports whether value uses numeric syntax that Go's
+// parsers accept and SQLite's numeric affinity does not convert: an underscore
+// separator, or the "0x" prefix that introduces a hexadecimal (and possibly
+// p-exponent) literal.
+func hasGoOnlyNumericSyntax(value string) bool {
+	digits := strings.TrimSpace(value)
+	digits = strings.TrimPrefix(strings.TrimPrefix(digits, "+"), "-")
+	if strings.Contains(digits, "_") {
+		return true
+	}
+	return len(digits) > 1 && digits[0] == '0' && (digits[1] == 'x' || digits[1] == 'X')
+}
+
 // isIntegerLiteralOverflowingInt64 reports whether value is an integer literal
 // (optional leading '+'/'-' followed solely by ASCII digits) whose magnitude
 // exceeds the range representable by int64. Such values can only be stored
@@ -697,6 +718,15 @@ func selectColumnType(typeCounts map[columnType]int, totalCount int) columnType
 		return columnTypeText
 	}
 
+	// A datetime is stored as text, so a column that also holds a number has no
+	// type covering both, exactly as a column holding text does. Picking the
+	// numeric one declared INTEGER or REAL over values SQLite then stored as
+	// text, leaving the schema and typeof() disagreeing.
+	if typeCounts[columnTypeDatetime] > 0 &&
+		typeCounts[columnTypeInteger]+typeCounts[columnTypeReal] > 0 {
+		return columnTypeText
+	}
+
 	// Calculate confidence for each type
 	datetimeConfidence := float64(typeCounts[columnTypeDatetime]) / float64(totalCount)
 	realConfidence := float64(typeCounts[columnTypeReal]) / float64(totalCount)

types_test.go

@@ -712,6 +712,17 @@ func TestIsFloat(t *testing.T) {
 		{"no digits", "abc", false},
 		{"multiple dots", "12.34.56", false},
 		{"invalid scientific", "1e", false},
+
+		// Go's parser accepts these spellings and SQLite's numeric affinity does
+		// not convert them. Calling them numeric declared a REAL column that
+		// stored every value as text, so the schema and typeof() disagreed.
+		{"underscore separators", "1_000", false},
+		{"underscore in a decimal", "1_000.5", false},
+		{"short underscore form", "1_0", false},
+		{"hexadecimal float", "0x1p4", false},
+		{"hexadecimal integer", "0x10", false},
+		{"binary literal", "0b101", false},
+		{"octal literal", "0o17", false},
 	}
 
 	for _, tt := range tests {
@@ -756,6 +767,31 @@ func TestSelectColumnType(t *testing.T) {
 			totalCount: 10,
 			expected:   columnTypeText,
 		},
+		{
+			// A datetime is stored as text, so a column holding one alongside a
+			// number has no type that covers both. Answering INTEGER declared a
+			// schema the storage did not match.
+			name: "datetime mixed with integer falls back to text",
+			typeCounts: map[columnType]int{
+				columnTypeInteger:  1,
+				columnTypeReal:     0,
+				columnTypeDatetime: 1,
+				columnTypeText:     0,
+			},
+			totalCount: 2,
+			expected:   columnTypeText,
+		},
+		{
+			name: "datetime mixed with real falls back to text",
+			typeCounts: map[columnType]int{
+				columnTypeInteger:  0,
+				columnTypeReal:     3,
+				columnTypeDatetime: 1,
+				columnTypeText:     0,
+			},
+			totalCount: 4,
+			expected:   columnTypeText,
+		},
 		{
 			name: "high confidence datetime",
 			typeCounts: map[columnType]int{
@@ -769,14 +805,27 @@ func TestSelectColumnType(t *testing.T) {
 		},
 		{
 			name: "low confidence fallback to most common",
+			typeCounts: map[columnType]int{
+				columnTypeInteger:  3,
+				columnTypeReal:     4,
+				columnTypeDatetime: 0,
+				columnTypeText:     0,
+			},
+			totalCount: 7,
+			expected:   columnTypeReal,
+		},
+		{
+			// REAL used to win this on confidence, and the two datetimes in it
+			// were then stored as text under a REAL declaration.
+			name: "low confidence numerics with a datetime fall back to text",
 			typeCounts: map[columnType]int{
 				columnTypeInteger:  3,
 				columnTypeReal:     4,
 				columnTypeDatetime: 2,
 				columnTypeText:     0,
 			},
 			totalCount: 10,
-			expected:   columnTypeReal,
+			expected:   columnTypeText,
 		},
 	}