fix: convert decimal to the type expected by go-mysql-server (#49)

binlogreplication/binlog_replication_alltypes_test.go

@@ -262,27 +262,27 @@ var allTypes = []typeDescription{
 			newTypeDescriptionAssertion("65535"),
 		},
 	},
-	// {
-	// 	TypeDefinition: "decimal",
-	// 	Assertions: [2]typeDescriptionAssertion{
-	// 		newTypeDescriptionAssertion("0"),
-	// 		newTypeDescriptionAssertion("1234567890"),
-	// 	},
-	// },
-	// {
-	// 	TypeDefinition: "decimal(10,2)",
-	// 	Assertions: [2]typeDescriptionAssertion{
-	// 		newTypeDescriptionAssertion("0.00"),
-	// 		newTypeDescriptionAssertion("12345678.00"),
-	// 	},
-	// },
-	// {
-	// 	TypeDefinition: "decimal(20,8)",
-	// 	Assertions: [2]typeDescriptionAssertion{
-	// 		newTypeDescriptionAssertion("-1234567890.12345678"),
-	// 		newTypeDescriptionAssertion("999999999999.00000001"),
-	// 	},
-	// },
+	{
+		TypeDefinition: "decimal",
+		Assertions: [2]typeDescriptionAssertion{
+			newTypeDescriptionAssertion("0"),
+			newTypeDescriptionAssertion("1234567890"),
+		},
+	},
+	{
+		TypeDefinition: "decimal(10,2)",
+		Assertions: [2]typeDescriptionAssertion{
+			newTypeDescriptionAssertion("0.00"),
+			newTypeDescriptionAssertion("12345678.00"),
+		},
+	},
+	{
+		TypeDefinition: "decimal(20,8)",
+		Assertions: [2]typeDescriptionAssertion{
+			newTypeDescriptionAssertion("-1234567890.12345678"),
+			newTypeDescriptionAssertion("999999999999.00000001"),
+		},
+	},
 
 	// Floating point types
 	{

executor.go

@@ -197,10 +197,7 @@ func (b *DuckBuilder) executeQuery(ctx *sql.Context, n sql.Node, conn *stdsql.Co
 		return nil, err
 	}
 
-	// Create a new iterator
-	iter := &SQLRowIter{rows: rows, schema: n.Schema()}
-
-	return iter, nil
+	return NewSQLRowIter(rows, n.Schema())
 }
 
 func (b *DuckBuilder) executeDML(ctx *sql.Context, n sql.Node, conn *stdsql.Conn) (sql.RowIter, error) {

iter.go

@@ -17,16 +17,45 @@ package main
 import (
 	stdsql "database/sql"
 	"io"
+	"strings"
 
 	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/marcboeker/go-duckdb"
+	"github.com/shopspring/decimal"
 )
 
 var _ sql.RowIter = (*SQLRowIter)(nil)
 
 // SQLRowIter wraps a standard sql.Rows as a RowIter.
 type SQLRowIter struct {
-	rows   *stdsql.Rows
-	schema sql.Schema
+	rows     *stdsql.Rows
+	columns  []*stdsql.ColumnType
+	schema   sql.Schema
+	buffer   []any // pre-allocated buffer for scanning values
+	pointers []any // pointers to the buffer
+	decimals []int
+}
+
+func NewSQLRowIter(rows *stdsql.Rows, schema sql.Schema) (*SQLRowIter, error) {
+	columns, err := rows.ColumnTypes()
+	if err != nil {
+		return nil, err
+	}
+
+	var decimals []int
+	for i, t := range columns {
+		if strings.HasPrefix(t.DatabaseTypeName(), "DECIMAL") {
+			decimals = append(decimals, i)
+		}
+	}
+
+	width := max(len(columns), len(schema))
+	buf := make([]any, width)
+	ptrs := make([]any, width)
+	for i := range buf {
+		ptrs[i] = &buf[i]
+	}
+	return &SQLRowIter{rows, columns, schema, buf, ptrs, decimals}, nil
 }
 
 // Next retrieves the next row. It will return io.EOF if it's the last row.
@@ -38,31 +67,34 @@ func (iter *SQLRowIter) Next(ctx *sql.Context) (sql.Row, error) {
 		return nil, io.EOF
 	}
 
-	columns, err := iter.rows.Columns()
-	if err != nil {
+	// Scan the values into the buffer
+	if err := iter.rows.Scan(iter.pointers[:len(iter.columns)]...); err != nil {
 		return nil, err
 	}
 
-	values := make([]interface{}, len(columns))
-	valuePtrs := make([]interface{}, len(columns))
-	for i := range values {
-		valuePtrs[i] = &values[i]
-	}
-
-	if err := iter.rows.Scan(valuePtrs...); err != nil {
-		return nil, err
+	// Process decimal values
+	for _, idx := range iter.decimals {
+		switch v := iter.buffer[idx].(type) {
+		case nil:
+			// nothing to do
+		case duckdb.Decimal:
+			iter.buffer[idx] = decimal.NewFromBigInt(v.Value, -int32(v.Scale))
+		case string:
+			iter.buffer[idx], _ = decimal.NewFromString(v)
+		default:
+			// nothing to do
+		}
 	}
 
-	// Prune the values to match the schema
-	if len(values) > len(iter.schema) {
-		values = values[:len(iter.schema)]
-	} else if len(values) < len(iter.schema) {
-		for i := len(values); i < len(iter.schema); i++ {
-			values = append(values, nil)
+	// Prune or fill the values to match the schema
+	width := len(iter.schema) // the desired width
+	if len(iter.columns) < width {
+		for i := len(iter.columns); i < width; i++ {
+			iter.buffer[i] = nil
 		}
 	}
 
-	return sql.NewRow(values...), nil
+	return sql.NewRow(iter.buffer[:width]...), nil
 }
 
 // Close closes the underlying sql.Rows.