src/Leevel/Database/Condition.php
protected function parseColumns(): string
    {
        if (empty($this->options['columns'])) {
            return '';
        }

        $columns = [];
        foreach ($this->options['columns'] as $item) {
            list($tableName, $col, $alias) = $item;

            // 表达式支持
            if (false !== strpos($col, '{') &&
                preg_match('/^{(.+?)}$/', $col, $matches)) {
                $columns[] = $this->connect->normalizeExpression(
                    $matches[1],
                    $tableName
                );
            } else {
                if ('*' !== $col && $alias) {
                    $columns[] = $this->connect->normalizeTableOrColumn(
                        "{$tableName}.{$col}", $alias, 'AS');
                } else {
                    $columns[] = $this->connect->normalizeTableOrColumn(
                        "{$tableName}.{$col}"
                    );
                }
            }
        }

        return implode(',', $columns);
    }
protected function parseColumns(): string
    {
        if (empty($this->options['columns'])) {
            return '';
        }

        $columns = [];
        foreach ($this->options['columns'] as $item) {
            list($tableName, $col, $alias) = $item;

            // 表达式支持
            if (false !== strpos($col, '{') &&
                preg_match('/^{(.+?)}$/', $col, $matches)) {
                $columns[] = $this->connect->normalizeExpression(
                    $matches[1],
                    $tableName
                );
            } else {
                if ('*' !== $col && $alias) {
                    $columns[] = $this->connect->normalizeTableOrColumn(
                        "{$tableName}.{$col}", $alias, 'AS');
                } else {
                    $columns[] = $this->connect->normalizeTableOrColumn(
                        "{$tableName}.{$col}"
                    );
                }
            }
        }

        return implode(',', $columns);
    }
分析语句中的字段.

@return string