mysql中的行转列

//查看当前商品库存

 function checkProductStock($product_id){
        global $wpdb;
        $sql="SELECT post_id,max(if((meta_key = '_stock_status'),meta_value,'')) AS stock_status,//此方法的作用
max(if((meta_key = '_manage_stock'),meta_value,'')) AS manage_stock,
max(if((meta_key = '_stock'),meta_value,'')) AS stock
from wp_postmeta WHERE post_id=".$product_id;
        $productStock=$wpdb->get_row($sql, ARRAY_A);
        $warehome=0;
        if(isset($productStock['stock_status']) && $productStock['stock_status']=='instock'){
            if(empty($productStock['manage_stock']) || $productStock['manage_stock']=='no'){
                $warehome=9999;
            }
            if(isset($productStock['manage_stock']) && $productStock['manage_stock']=='yes' && isset($productStock['stock']) && $productStock['stock']>0){
                $warehome=$productStock['stock'];
            }
        }
        return $warehome;
    }