Method parseSelectStatement

pkg/sql/parser/select.go:36–213

parseSelectStatement parses a SELECT statement. It delegates each clause to a focused helper method.

()

// parseSelectStatement parses a SELECT statement.
// It delegates each clause to a focused helper method.
func (p *Parser) parseSelectStatement() (ast.Statement, error) {
	// We've already consumed the SELECT token in matchType.

	// DISTINCT / ALL modifier
	isDistinct, distinctOnColumns, err := p.parseDistinctModifier()
	if err != nil {
		return nil, err
	}

	// Reject TOP in dialects that use LIMIT/OFFSET or ROWNUM/FETCH FIRST instead.
	// String comparison is used here because the lexer has no TokenTypeTOP constant;
	// TOP is emitted as an identifier literal (see parseTopClause comment).
	nonTopDialects := map[string]bool{
		string(keywords.DialectMySQL):      true,
		string(keywords.DialectPostgreSQL): true,
		string(keywords.DialectSQLite):     true,
		string(keywords.DialectOracle):     true,
	}
	if nonTopDialects[p.dialect] && strings.ToUpper(p.currentToken.Token.Value) == "TOP" {
		if p.dialect == string(keywords.DialectOracle) {
			return nil, fmt.Errorf("TOP clause is not supported in Oracle; use ROWNUM or FETCH FIRST … ROWS ONLY instead")
		}
		return nil, fmt.Errorf("TOP clause is not supported in %s; use LIMIT/OFFSET instead", p.dialect)
	}

	// SQL Server TOP clause
	topClause, err := p.parseTopClause()
	if err != nil {
		return nil, err
	}

	// Column list
	columns, err := p.parseSelectColumnList()
	if err != nil {
		return nil, err
	}

	// FROM … JOIN clauses
	tableName, tables, joins, err := p.parseFromClause()
	if err != nil {
		return nil, err
	}

	// Initialise the statement early so clause parsers can check dialect etc.
	selectStmt := &ast.SelectStatement{
		Distinct:          isDistinct,
		DistinctOnColumns: distinctOnColumns,
		Top:               topClause,
		Columns:           columns,
		From:              tables,
		Joins:             joins,
		TableName:         tableName,
	}

	// SAMPLE (ClickHouse-specific, specifies sampling rate/size; comes after FROM/FINAL)
	if p.dialect == string(keywords.DialectClickHouse) && p.isTokenMatch("SAMPLE") {
		if selectStmt.Sample, err = p.parseSampleClause(); err != nil {
			return nil, err