1、判斷字段不存在則增加該字段
Talk is cheap, show me your code!
-- [新增]判斷字段不存在則增加該字段
drop procedure if exists proc_add_column_unless_exist;
delimiter $$
create procedure proc_add_column_unless_exist(in var_table_name varchar(64),in var_column_name varchar(64),in var_sqlstr varchar(1024))
top:begin
-- 表不存在則直接返回
set @p_tablenum='';
set @sqlstr1=concat('select count(table_name)into @p_tablenum from information_schema.tables where table_schema=database() and table_name=\'',var_table_name,'\' limit 1;');
prepare stmt1 from @sqlstr1;
execute stmt1;
deallocate prepare stmt1;
if(@p_tablenum<1)then
leave top;
end if;
-- 字段已存在則直接返回
set @p_columnnum='';
set @sqlstr=concat('select count(column_name) into @p_columnnum from information_schema.columns where table_schema=database() and table_name=\'',var_table_name,'\'and column_name =\'',var_column_name,'\';');
prepare stmt2 from @sqlstr;
execute stmt2;
deallocate prepare stmt2;
if(@p_columnnum>0)then
leave top;
end if;
-- 表存在且字段不存在則創建新字段
set @sqlcmd=var_sqlstr;
prepare stmt3 from @sqlcmd;
execute stmt3;
deallocate prepare stmt3;
end $$
delimiter;
2、修改表字段的函數,有則修改,無則不修改
-- [新增]修改表字段的函數
drop procedure if exists proc_modify_column_unless_exist;
delimiter $$
create procedure proc_modify_column_unless_exist(in var_table_name varchar(64),in var_column_name varchar(64),in var_sqlstr varchar(1000))
top:begin
-- 表不存在則直接返回
set @p_tablenum='';
set @sqlstr1=concat('select count(table_name)into @p_tablenum from information_schema.tables where table_schema=database) and table name=\'',var_table_name, '\'limit 1;');
prepare stmt1 from @sqlstr1;
execute stmt1;
deallocate prepare stmt1;
if(@p_tablenum<1)then
leave top;
end if;
-- 字段不存在則直接返回
set @p_columnnum='';
set @sqlstr=concat('select count(column_name)into @p_columnnum from information_schema.columns where table_schema=database() and table_name=\'',var_table_name, '\'and column_name=\'',var_column_name,'\';');
prepare stmt2 from @sqlst;
execute stmt2;
deallocate prepare stmt2;
if(@p_columnnum <=0)then
leave top;
end if;
-- 表存在且字段存在則修改字段
set @sqlcmd=var_sqlstr;
prepare stmt3 from @sqlcmd;
execute stmt3;
deallocate prepare stmt3;
end $$
delimiter;
知識點補充:
1、declare和set定義變量的區別?
declare(稱爲存儲過程變量)定義的類似是局部變量,declare僅在方法中生效,即只在存儲過程中的begin和end之間生效;,set(稱爲會話變量)定義的類似全局變量,,即這個變量可以在被調用的存儲過程或者代碼之間共享數據,變量面前必須加@符號(@是用戶自定義變量,@@是系統定義變量)。
2、查出該表有哪些索引,索引名-->集合
SHOW INDEX FROM t_emp
元數據:meta DATA 描述數據的數據SELECT index_name FROM information_schema.STATISTICS WHERE table_name='t_emp' AND table_schema='mydb'
AND index_name <>'PRIMARY' AND seq_in_index = 1
3、 如何循環集合
CURSOR 遊標
FETCH xxx INTO xxx
4、如何讓mysql執行一個字符串
PREPARE 預編譯 XXXEXECUTE
5、執行存儲過程
CALL proc_drop_index ('mydb','t_emp');