sql/mssql: inspect column default value (#1782)

sql/mssql/inspect.go

@@ -280,14 +280,15 @@ func (i *inspect) addColumn(s *schema.Schema, rows *sql.Rows, scope queryScope)
 		nullable, userDefined                     sql.NullInt64
 		identity, identitySeek, identityIncrement sql.NullInt64
 		size, precision, scale, isPersisted       sql.NullInt64
-		genexpr                                   sql.NullString
+		genexpr, defaults                         sql.NullString
 		isComputed                                int64
 	)
 	if err = rows.Scan(
 		&table, &name, &typeName, &comment,
 		&nullable, &userDefined,
 		&identity, &identitySeek, &identityIncrement,
-		&collation, &size, &precision, &scale, &isComputed, &genexpr, &isPersisted,
+		&collation, &size, &precision, &scale, &isComputed,
+		&genexpr, &isPersisted, &defaults,
 	); err != nil {
 		return err
 	}
@@ -323,6 +324,9 @@ func (i *inspect) addColumn(s *schema.Schema, rows *sql.Rows, scope queryScope)
 		}
 		c.SetGeneratedExpr(x)
 	}
+	if defaults.Valid {
+		c.Default = i.defaultExpr(c, defaults.String)
+	}
 	if sqlx.ValidString(comment) {
 		c.SetComment(comment.String)
 	}
@@ -439,6 +443,29 @@ func nArgs(start, n int) string {
 	return b.String()
 }
 
+// defaultExpr returns the default expression of the given column.
+//
+// https://learn.microsoft.com/en-us/sql/relational-databases/tables/specify-default-values-for-columns
+func (i *inspect) defaultExpr(_ *schema.Column, x string) schema.Expr {
+	// Remove the parenthesis from the expression.
+	x = mayUnwrap(x)
+	// Literal expression is quoted or wrapped with parenthesis.
+	if sqlx.IsQuoted(x, '\'') || mayUnwrap(x) != x {
+		return &schema.Literal{V: x}
+	}
+	// Raw expression does not have a parenthesis.
+	return &schema.RawExpr{X: x}
+}
+
+// mayUnwrap removes the wrapping parentheses from the given string.
+func mayUnwrap(s string) string {
+	n := len(s) - 1
+	if len(s) < 2 || s[0] != '(' || s[n] != ')' {
+		return s
+	}
+	return s[1:n]
+}
+
 const (
 	// Query to list server properties.
 	propertiesQuery = "SELECT SERVERPROPERTY('ProductVersion'), SERVERPROPERTY('Collation'), SERVERPROPERTY('SqlCharSetName')"
@@ -532,7 +559,8 @@ SELECT
 	[scale] = [c1].[scale],
 	[is_computed] = [c1].[is_computed],
 	[computed_definition] = [cc].[definition],
-	[computed_persisted] = [cc].[is_persisted]
+	[computed_persisted] = [cc].[is_persisted],
+	[default_definition] = [dc].[definition]
 FROM
 	[sys].[tables] [t1]
 	INNER JOIN [sys].[columns] [c1]
@@ -542,6 +570,10 @@ FROM
 	LEFT JOIN [sys].[computed_columns] [cc]
 	ON [cc].[object_id] = [c1].[object_id]
 	AND [cc].[column_id] = [c1].[column_id]
+	LEFT JOIN [sys].[default_constraints] [dc]
+	ON [dc].[object_id] = [c1].[default_object_id]
+	AND [dc].[parent_object_id] = [c1].[object_id]
+	AND [dc].[parent_column_id] = [c1].[column_id]
 	LEFT JOIN [sys].[identity_columns] [ti]
 	ON [ti].[object_id] = [c1].[object_id]
 	AND [ti].[column_id] = [c1].[column_id]