SQL笔记
SQL优化
1.避免使用select *
2.union all 代替 union
union all 可以获取所有数据，包括重复数据
union 会排重，其过程需要遍历排序和比较 更耗时、更消耗CPU资源
3.小表驱动大表
4.批量操作尽量不要用for循环
SQL虚拟表
select * from dual
当前时间
sysdate
下划线转驼峰
# 控制台输出sql、下划线转驼峰
mybatis:
configuration:
log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
map-underscore-to-camel-case: true
1. 设置传参、定义局部变量、局部变量赋值
ALTER PROCEDURE [dbo].[test]
@ID VARCHAR(100) --执行存储过程的传参
AS
BEGIN TRY
declare @COUNTA int; -- 定义全局存储过程参数
set @COUNTA = (select COUNT(*) from APP_BATCH_JOB_LOG); -- 给参数赋值
if @ID>@COUNTA -- if判断
select COUNT(*) as id from APP_BATCH_JOB_LOG;
else
select * from APP_BATCH_JOB_LOG where id = @id;
END
2.try catch
begin try
--SQL
end try
begin catch
--sql (处理出错动作)
end catch
时间转换
https://www.cnblogs.com/damugua/p/14681300.html
取正数
SELECT ABS(-**123**); -- 123
# SQL拼接
```sql
可以传好几个参数
concat(cast(isnull(b.AVERAGE_RATE,0.0) as numeric(20,2)),'%')as AVERAGE_RATE
SELECT concat(code,'-',DESCRIPTION) FROM RP_D_REPORTLINE
取年
SELECT
datepart(yy,DATEADD(YEAR,-1,asof_date)) as lastYear,
datepart(yy,asof_date) as year
from RP_S_ASOFDATE
强转位小数
*Convert**(*decimal*(*18,2*)*,rd.AMOUNT*)* as AMOUNT,
删除表某个字段
ALTER TABLE FMD_ADB DROP COLUMN ID;
ALTER TABLE a表 DROP COLUMN a表的某个字段;
# 添加某个字段
```sql
ALTER TABLE FMD_ADB add COLUMN ID;
--- 对的
ALTER TABLE 表名 ADD字段名 nvarchar(200)
修改字段长度
alter table Table1 alter column Column1 varchar(10)
两表合并
select count*(***)* from T_FMDDATA_T24 union all
select count*(***)* from FBNK_LIMIT_T24 union all
select count*(***)* from T_TRIAL_BALANCE_T24
存储过程执行某个字段里的SQL语句
ALTER PROCEDURE [dbo].[aa]
AS
BEGIN
create table #tmp(
number int,
code int,
name NVARCHAR(200)
)
DECLARE @sqlMain NVARCHAR(4000),@balance_usd INT
declare my_cursor cursor for
SELECT code FROM RP_D_DEPARTMENT
open my_cursor
DECLARE @dept NVARCHAR(50);
DECLARE @numb NVARCHAR(50);
DECLARE @name NVARCHAR(200);
fetch next from my_cursor into @dept
while @@FETCH_STATUS=0
begin
-- routine body goes here, e.g.
-- SELECT 'Navicat for SQL Server'
SELECT @sqlMain = REPLACE(concat('set @balance_usd= (',db_dyn_sql,')'),'${department}',@dept )FROM jimu_report_db WHERE jimu_report_id = '707485132628443136' and db_ch_name = 'dca'
execute sp_executesql @sqlMain,N'@balance_usd NUMERIC(38,8) output',@balance_usd OUTPUT
--select @name = name from RP_D_DEPARTMENT where cdoe = @dept
select @name= name from RP_D_DEPARTMENT where CODE = @dept
INSERT INTO #tmp VALUES (@balance_usd,@dept,@name)
fetch next from my_cursor into @dept --获取下一条数据并赋值给变量
end--关闭释放游标
close my_cursor;
deallocate my_cursor;
select * from #tmp
END
# 创建索引
1、使用CREATE INDEX创建，语法如下：
CREATE INDEX indexName ON tableName (columnName(length));
2、使用ALTER语句创建，语法如下：
ALTER TABLE tableName ADD INDEX indexName(columnName);
ALTER语句创建索引，下面提供一个设置索引长度的例子：
ALTER TABLE t_user_action_log ADD INDEX ip_address_idx (ip_address(16));
SHOW INDEX FROM t_user_action_log;
3、建表的时候创建索引
CREATE TABLE tableName(
id INT NOT NULL,
columnName columnType,
INDEX [indexName] (columnName(length))
);
示例：
X ip_address_idx (ip_address(16));
SHOW INDEX FROM t_user_action_log;
3、建表的时候创建索引
```sql
CREATE TABLE tableName(
id INT NOT NULL,
columnName columnType,
INDEX [indexName] (columnName(length))
);