Method parse_optional_table_constraint

src/sql-parser/src/parser.rs:5452–5519

(
        &mut self,
    )

    }

    fn parse_optional_table_constraint(
        &mut self,
    ) -> Result<Option<TableConstraint<Raw>>, ParserError> {
        let name = if self.parse_keyword(CONSTRAINT) {
            Some(self.parse_identifier()?)
        } else {
            None
        };
        match self.next_token() {
            Some(Token::Keyword(PRIMARY)) => {
                self.expect_keyword(KEY)?;
                let columns = self.parse_parenthesized_column_list(Mandatory)?;
                Ok(Some(TableConstraint::Unique {
                    name,
                    columns,
                    is_primary: true,
                    nulls_not_distinct: false,
                }))
            }
            Some(Token::Keyword(UNIQUE)) => {
                let nulls_not_distinct = if self.parse_keyword(NULLS) {
                    self.expect_keywords(&[NOT, DISTINCT])?;
                    true
                } else {
                    false
                };

                let columns = self.parse_parenthesized_column_list(Mandatory)?;
                Ok(Some(TableConstraint::Unique {
                    name,
                    columns,
                    is_primary: false,
                    nulls_not_distinct,
                }))
            }
            Some(Token::Keyword(FOREIGN)) => {
                self.expect_keyword(KEY)?;
                let columns = self.parse_parenthesized_column_list(Mandatory)?;
                self.expect_keyword(REFERENCES)?;
                let foreign_table = self.parse_raw_name()?;
                let referred_columns = self.parse_parenthesized_column_list(Mandatory)?;
                Ok(Some(TableConstraint::ForeignKey {
                    name,
                    columns,
                    foreign_table,
                    referred_columns,
                }))
            }
            Some(Token::Keyword(CHECK)) => {
                self.expect_token(&Token::LParen)?;
                let expr = Box::new(self.parse_expr()?);
                self.expect_token(&Token::RParen)?;
                Ok(Some(TableConstraint::Check { name, expr }))
            }
            unexpected => {
                if name.is_some() {
                    self.expected(
                        self.peek_prev_pos(),