一、查詢語句
1、字串擷取：

update sys_area set short_name = substring_index(short_name, '地區', 1) where type = 3 and short_name is not null and short_name like '%地區'

substring(str, pos); substring(str, pos, len)

2、rowNum實現

SELECT @rownum:[email protected]num+1 rownum, CollectSn From
(SELECT @rownum:=0
 
,bbgmain.* FROM qbdb.bbgmain WHERE collectsn!='' ORDER BY collectsn limit 10) t

3、獲取分組中最新的資訊
mysql執行順序：
寫的順序：select … from… where…. group by… having… order by..
執行順序：from… where…group by… having…. select … order by…
所以group by到select時只取到分組裡的第一條資訊
解決方法：
- where+group by（對小組進行排序）

select * from
 
 `test` where id in(select SUBSTRING_INDEX(group_concat(id order by `date` desc),',',1) from `test` group by category_id ) order by `date` desc

• 從form返回的資料下手腳（即用子查詢）

select * from (select * from `test` order by `date` desc) `temp`  group by category_id order by `date` desc

5、查詢重複欄位

1、查詢表中多餘的重複記錄，重複記錄是根據單個欄位（peopleId）來判斷
select
 
 * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

2、刪除表中多餘的重複記錄，重複記錄是根據單個欄位（peopleId）來判斷，只留有rowid最小的記錄
delete from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)

3、查詢表中多餘的重複記錄（多個欄位）
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

4、刪除表中多餘的重複記錄（多個欄位），只留有rowid最小的記錄
delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)

5、查詢表中多餘的重複記錄（多個欄位），不包含rowid最小的記錄
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)

6、MySQL order null 0 - 把null和0(零)排在最後

SELECT `vcenter_ip`, `status`, `sla_id` FROM vm_list ORDER BY sla_id is NULL, sla_id = 0, sla_id ASC;

7、獲取上一次插入的自增id

select LAST_INSERT_ID()

二、資料庫更新
1、根據查詢出來的值更新表多個欄位

UPDATE student D
  LEFT JOIN (SELECT 
        B.studentId,
                SUM(B.score) AS s_sum,
                ROUND(AVG(B.score),1) AS s_avg
           FROM score B
          WHERE b.examTime >= '2015-03-10'
          GROUP BY B.studentId) C
    ON (C.studentId = D.id)

   SET D.score_sum = c.s_sum,
       D.score_avg = c.s_avg
 WHERE D.id = ''

三、資料庫插入
1、批量插入

INSERT INTO `insert_table` (`datetime`, `uid`, `content`, `type`)   VALUES ('0', 'userid_0', 'content_0', 0), ('1', 'userid_1', 'content_1', 1);

四、資料庫功能
2、資料庫定時：

SHOW VARIABLES LIKE 'event_scheduler';
SET GLOBAL event_scheduler = ON;

3、表結構分析

select * from go_run_record procedure analyse();

4、儲存過程

DROP PROCEDURE IF EXISTS `p_update_praise_week`;
DELIMITER ;;
CREATE PROCEDURE p_update_praise_week()
BEGIN
        DECLARE w_user_id VARCHAR(64);
        DECLARE w_count INT;
        DECLARE h_user_id VARCHAR(64);
        DECLARE stops INT DEFAULT 0;

        DECLARE cur_account CURSOR FOR select a.user_id,a.count from go_user_praise_week a where a.del_flag = 0;

    DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET stops=1;
    OPEN cur_account;     

    read_loop: LOOP
                SET stops = 0;
        FETCH NEXT from cur_account INTO w_user_id,w_count;
                if stops = 1 then
                    leave read_loop;
                end if;

                select a.user_id into h_user_id from go_user_praise_history a where a.user_id = w_user_id and a.del_flag = 0;

                if h_user_id is null then
                    insert go_user_praise_history values(w_user_id,w_count,now(),'0',now());
                ELSE
                    update go_user_praise_history set `count` = `count` + w_count where user_id = w_user_id;
                end if;

    END LOOP;
    CLOSE cur_account;
END
;
DELIMITER ;

執行動態sql

--儲存過程名和引數，引數中in表示傳入引數，out標示傳出引數，inout表示傳入傳出引數

create procedure p_procedurecode(in sumdate varchar(10))   
begin
     declare v_sql varchar(500);    --需要執行的SQL語句
     declare sym varchar(6);

     declare var1 varchar(20);
     declare var2 varchar(70);
     declare var3 integer;

     --定義遊標遍歷時，作為判斷是否遍歷完全部記錄的標記
     declare no_more_departments integer DEFAULT 0;     

     --定義遊標名字為C_RESULT 
     DECLARE C_RESULT CURSOR FOR
             SELECT barcode,barname,barnum FROM tmp_table;

    --聲明當遊標遍歷完全部記錄後將標誌變數置成某個值
     DECLARE CONTINUE HANDLER FOR NOT FOUND
             SET no_more_departments=1;

     set sym=substring(sumdate,1,6);     --擷取字串，並將其賦值給一個遍歷

     --連線字串構成完整SQL語句，動態SQL執行後的結果記錄集，在MySQL中無法獲取，因此需要轉變思路將其放置到一個臨時表中（注意程式碼中的寫法）。一般寫法如下：

     --     'Create TEMPORARY Table   表名（Select的查詢語句）;
     set v_sql= concat('Create TEMPORARY Table tmp_table(select aa as aacode,bb as aaname,count(cc) as ccnum from h',sym,' where substring(dd,1,8)=''',sumdate,''' group by aa,bb)');

     set @v_sql=v_sql;   --注意很重要，將連成成的字串賦值給一個變數（可以之前沒有定義，但要以@開頭）
     prepare stmt from @v_sql;  --預處理需要執行的動態SQL，其中stmt是一個變數
     EXECUTE stmt;      --執行SQL語句
     deallocate prepare stmt;     --釋放掉預處理段

     OPEN C_RESULT;       --開啟之前定義的遊標
     REPEAT                      --迴圈語句的關鍵詞
           FETCH C_RESULT INTO VAR1, VAR2, VAR3;   --取出每條記錄並賦值給相關變數，注意順序

          --執行查詢語句，並將獲得的值付給一個變數 @oldaacode（注意如果以@開頭的變數可以不用通過declare語句事先宣告）
           select @oldaacode:=vcaaCode from T_sum where vcaaCode=var1 and dtDate=sumdate; 
           if @oldaacode=var1 then    --判斷
              update T_sum set iNum=var3 where vcaaCode=var1 and dtDate=sumdate;
           else
               insert into T_sum(vcaaCode,vcaaName,iNum,dtDate) values(var1,var2,var3,sumdate);
           end if;
     UNTIL no_more_departments  END REPEAT;    --迴圈語句結束
     CLOSE C_RESULT;                            --關閉遊標

     DROP TEMPORARY TABLE tmp_table;       --刪除臨時表
end;

5、觸發器
新資料：new.欄位名，舊資料：old.欄位名

DROP TRIGGER IF EXISTS t_afterinsert_on_record;
CREATE TRIGGER t_afterinsert_on_record 
AFTER INSERT ON go_run_record
FOR EACH ROW
BEGIN

end;