IFNULL(_receipt_all.yyyy,YEAR (NOW()))yyyy,

这是一个SQL语句中的表达式，大致的意思是：如果_receipt_all表中的yyyy列不为空，则返回yyyy列的值，否则返回当前时间的年份。

具体解释如下：

- IFNULL(expr1, expr2) 函数：如果expr1不为NULL，则返回expr1的值，否则返回expr2的值。
- _receipt_all.yyyy：表示_receipt_all表中的yyyy列。
- YEAR(NOW())：是MySQL中的一个内置函数，用于返回当前时间的年份。

因此，IFNULL(_receipt_all.yyyy,YEAR (NOW()))的含义是，如果_receipt_all表中yyyy列不为空，则返回yyyy列的值，否则返回当前时间的年份。最后加上"yyyy"，表示将结果命名为"yyyy"。

相关问题

IFNULL( sum(_receipt_all.amount), 0 ) amount

这是一个SQL语句中的表达式，大致的意思是：如果_receipt_all表中的amount列的和不为NULL，则返回amount列的和，否则返回0。

具体解释如下：

- IFNULL(expr1, expr2) 函数：如果expr1不为NULL，则返回expr1的值，否则返回expr2的值。
- SUM(expr) 函数：是MySQL中的一个聚合函数，用于计算指定列的总和。
- _receipt_all.amount：表示_receipt_all表中的amount列。
- 0：表示当_receipt_all表中的amount列的和为NULL时，返回的默认值。

因此，IFNULL(sum(_receipt_all.amount), 0)的含义是，如果_receipt_all表中amount列的和不为NULL，则返回amount列的和，否则返回0。最后加上"amount"，表示将结果命名为"amount"。

优化以下SQL select pao.id, pao.order_no, pao.apply_time, pao.purchase_user_id, pao.purchase_user_name, pao.apply_user_id, pao.apply_user_name, pao.apply_department_id, pao.apply_department_name, pao.apply_end_time, pao.create_user_id, pao.create_user_name, pao.approve_type, pao.approve_user_id, pao.approve_user_name, pao.approve_time, pao.description, pao.order_type, pao.purchase_type, pao.storage_type, pao.compose_order_no, pao.company_id, pao.delete, pao.create_time, pao.update_time, pao.supplier_id, pao.image_path, pao.contract_id, pao.status, pao.invoice_signer_name, pao.total_amount, pao.total_amount_tax, pao.purchase_status, pao.cancel_reason, pao.print_status, pao.demand_id, pao.arrival_status, pao.supervise_num, pao.supervise_date, pao.merge_apply_id, pao.deadline, pao.remind , s.name as supplierName, paod.amount, cm.return_status as returnStatus, cm.inventory_status as inventoryStatus, cm.stock_remark, cm.merge_flag, cm.signature_file, cm.department_pass, cm.receipt_file, cm.amount_paid, cm.amount_unpaid, cm.contract_name, cm.status as contractStatus, cm.contract_no, cm.contract_amount, paod.product_name, cm.advance_payment, cm.advance_ratio, cm.currency_unit from purchase_apply_order pao left join supplier s on pao.supplier_id = s.id left join ( SELECT GROUP_CONCAT(distinct p.product_name) product_name, sum(IFNULL(amount_tax, 0)) amount, apply_order_no from purchase_apply_order_details pa left join product p on p.pn_code = pa.product_code where p.company_id = 29 GROUP BY apply_order_no ) paod on paod.apply_order_no = pao.order_no left join contract_management cm on pao.contract_id = cm.id where pao.delete = 0 and pao.company_id = 29 and deadline <= '2023-05-25 15:34:00.01' and remind = 0 and arrival_status in( 0 , 1 ) order by pao.create_time desc;

首先，我们可以对该 SQL 查询语句进行简化，只选择需要的字段而不是全部选择。其次，我们可以尝试添加索引以加快查询速度。

以下是优化后的 SQL 查询语句：

SELECT pao.id, pao.order_no, pao.apply_time, pao.purchase_user_id, pao.purchase_user_name, pao.apply_user_id, 
       pao.apply_user_name, pao.apply_department_id, pao.apply_department_name, pao.apply_end_time, pao.create_user_id, 
       pao.create_user_name, pao.approve_type, pao.approve_user_id, pao.approve_user_name, pao.approve_time, 
       pao.description, pao.order_type, pao.purchase_type, pao.storage_type, pao.compose_order_no, pao.company_id, 
       pao.delete, pao.create_time, pao.update_time, pao.supplier_id, pao.image_path, pao.contract_id, pao.status, 
       pao.invoice_signer_name, pao.total_amount, pao.total_amount_tax, pao.purchase_status, pao.cancel_reason, 
       pao.print_status, pao.demand_id, pao.arrival_status, pao.supervise_num, pao.supervise_date, pao.merge_apply_id, 
       pao.deadline, pao.remind, s.name AS supplierName, paod.amount, cm.return_status AS returnStatus, 
       cm.inventory_status AS inventoryStatus, cm.stock_remark, cm.merge_flag, cm.signature_file, cm.department_pass, 
       cm.receipt_file, cm.amount_paid, cm.amount_unpaid, cm.contract_name, cm.status AS contractStatus, 
       cm.contract_no, cm.contract_amount, paod.product_name, cm.advance_payment, cm.advance_ratio, cm.currency_unit
FROM purchase_apply_order pao 
LEFT JOIN supplier s ON pao.supplier_id = s.id 
LEFT JOIN (
    SELECT GROUP_CONCAT(DISTINCT p.product_name) product_name, SUM(IFNULL(amount_tax, 0)) amount, apply_order_no 
    FROM purchase_apply_order_details pa 
    LEFT JOIN product p ON p.pn_code = pa.product_code 
    WHERE p.company_id = 29 
    GROUP BY apply_order_no 
) paod ON paod.apply_order_no = pao.order_no 
LEFT JOIN contract_management cm ON pao.contract_id = cm.id 
WHERE pao.delete = 0 
  AND pao.company_id = 29 
  AND deadline <= '2023-05-25 15:34:00.01' 
  AND remind = 0 
  AND arrival_status IN (0, 1) 
ORDER BY pao.create_time DESC;

我们可以为 `purchase_apply_order` 表的 `company_id` 字段和 `deadline` 字段以及 `remind` 字段创建索引。同时，也可以为 `arrival_status` 字段和 `delete` 字段创建索引。这可以大大加快查询速度。

CREATE INDEX idx_purchase_apply_order_company_id_deadline_remind ON purchase_apply_order (company_id, deadline, remind);

CREATE INDEX idx_purchase_apply_order_arrival_status_delete ON purchase_apply_order (arrival_status, delete);