Method parseJoinCondition

pkg/sql/parser/select_clauses.go:259–310

parseJoinCondition parses the ON / USING clause that follows a joined table reference. CROSS JOIN, APPLY, and NATURAL JOIN variants do not require a condition.

(joinType string, isNatural, isApply bool)

// parseJoinCondition parses the ON / USING clause that follows a joined table reference.
// CROSS JOIN, APPLY, and NATURAL JOIN variants do not require a condition.
func (p *Parser) parseJoinCondition(joinType string, isNatural, isApply bool) (ast.Expression, error) {
	isCrossJoin := joinType == "CROSS" || isApply
	if isCrossJoin || isNatural {
		return nil, nil
	}

	if p.isType(models.TokenTypeOn) {
		p.advance() // Consume ON
		cond, err := p.parseExpression()
		if err != nil {
			return nil, goerrors.InvalidSyntaxError(
				fmt.Sprintf("error parsing ON condition for %s JOIN: %v", joinType, err),
				p.currentLocation(),
				"",
			)
		}
		return cond, nil
	}

	if p.isType(models.TokenTypeUsing) {
		p.advance() // Consume USING
		if !p.isType(models.TokenTypeLParen) {
			return nil, p.expectedError("( after USING")
		}
		p.advance()

		var usingColumns []ast.Expression
		for {
			if !p.isIdentifier() {
				return nil, p.expectedError("column name in USING")
			}
			usingColumns = append(usingColumns, &ast.Identifier{Name: p.currentToken.Token.Value})
			p.advance()
			if !p.isType(models.TokenTypeComma) {
				break
			}
			p.advance()
		}

		if !p.isType(models.TokenTypeRParen) {
			return nil, p.expectedError(") after USING column list")
		}
		p.advance()

		if len(usingColumns) == 1 {
			return usingColumns[0], nil
		}
		return &ast.ListExpression{Values: usingColumns}, nil
	}

	return nil, p.expectedError("ON or USING")
}

// parseSampleClause parses the ClickHouse SAMPLE clause that specifies data sampling.
// It is called when the current token is SAMPLE (already verified by caller).