1，代碼塊
代碼順序

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1，變量和條件聲明???
2，Cursor聲明???
3，Handler聲明???
4，程序代碼??

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可以給代碼塊加lebel，這樣END匹配比較直觀，還可以用LEAVE語句來終結代碼塊:

[label:]?BEGIN???
????varaiable?and?condition?declarations???
????cursor?declarations???
????handler?declarations???
??
????program?code???
END?[label];??

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代碼塊可以嵌套:

代碼 CREATE?PROCEDURE?nested_blocks()???
BEGIN???
????DECLARE?my_variable?varchar(20);???
????SET?my_variable='This?value?was?set?in?the?outer?block';???
????BEGIN???
????????SET?my_variable='This?value?was?set?in?the?inner?block';???
????END;???
????SELECT?my_variable,?'Changes?in?the?inner?block?are?visible?in?the?outer?block';???
END;?

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LEAVE的例子:

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代碼 CREATE?PROCEDURE?nested_blocks()???
outer_block:?BEGIN???
????DECLARE?l_status?int;???
????SET?l_status=1;???
????inner_block:?BEGIN???
????????IF?(l_status=1)?THEN???
????????????LEAVE?inner_block;???
????????END?IF;???
????????SELECT?'This?statement?will?never?be?executed';???
????END?inner_block;???
????SELECT?'End?of?program';???
END?outer_block;??

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2，條件控制
IF:

IF?expression?THEN?commands???
????[ELSEIF?expression?THEN?commands]???
????[ELSE?commands]???
END?IF;?

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例子:

代碼 IF?(sale_value?>?200)?THEN???
????CALL?free_shipping(sale_id);????/*Free?shipping*/??
????IF?(customer_status='PLATINUM')?THEN???
????????CALL?apply_discount(sale_id,20);?/*?20%?discount?*/??
????ELSEIF?(customer_status='GOLD')?THEN???
????????CALL?apply_discount(sale_id,15);?/*?15%?discount?*/??
????ELSEIF?(customer_status='SILVER')?THEN???
????????CALL?apply_discount(sale_id,10);?/*?10%?discount?*/??
????ELSEIF?(customer_status='BRONZE')?THEN???
????????CALL?apply_discount(sale_id,5);?/*?5%?discount*/??
????END?IF;???
END?IF;??

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CASE:

CASE???
????WHEN?condition?THEN???
????????statements???
????[WHEN?condition?THEN???
????????statements...]???
????[ELSE???
????????statements]???
END?CASE;??

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例子:

代碼 CASE???
????WHEN?(sale_value>200)?THEN???
????????CALL?free_shipping(sale_id);???
????????CASE?customer_status???
????????????WHEN?'PLATINUM'?THEN???
????????????????CALL?apply_discount(sale_id,20);???
????????????WHEN?'GOLD'?THEN???
????????????????CALL?apply_discount(sale_id,15);???
????????????WHEN?'SILVER'?THEN???
????????????????CALL?apply_discount(sale_id,10);???
????????????WHEN?'BRONZE'?THEN???
????????????????CALL?apply_discount(sale_id,5);???
????????END?CASE;???
END?CASE;??

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CASE與SELECT語句結合的妙用:

SELECT?(CASE?WHEN?(t.a?=?1?AND?t.b?=?0)?THEN?t.c?ELSE?'N/A'?END)?AS?result?FROM?test?t?order?by?result?asc??

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3，迭代
LOOP

[label:]?LOOP???
????statements???
END?LOOP?[label];??

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REPEAT...UNTIL

[label:]?REPEAT???
????statements???
UNTIL?expression???
END?REPEAT?[label]??

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WHILE

[label:]?WHILE?expression?DO???
????statements???
END?WHILE?[label]??

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LEAVE語句

SET?i=1;???
myloop:?LOOP???
????SET?i=i+1;???
????IF?i=10?then???
????????LEAVE?myloop;???
????END?IF:???
END?LOOP?myloop;???
SELECT?'I?can?count?to?10';??

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ITERATE語句

代碼 SET?i=0;???
loop1:?LOOP???
????SET?i=i+1;???
????IF?i>=10?THEN?????????????????/*Last?number?-?exit?loop*/??
????????LEAVE?loop1;???
????ELSEIF?MOD(i,?2)=0?THEN???????/*Even?number?-?try?again*/??
????????ITERATE?loop1;???
????END?IF;???
??
????SELECT?CONCAT(i,?"?is?an?odd?number");???
END?LOOP?loop1;??

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嵌套循環

代碼 DECLARE?i,?j?INT?DEFAULT?1;???
outer_loop:?LOOP???
????SET?j=1;???
????inner_loop:?LOOP???
????????SELECT?concat(i,?"?times?",?j,?"?is?",?i*j);???
????????SET?j=j+1;???
????????IF?j>12?THEN???
????????????LEAVE?inner_loop;???
????????END?IF;???
????END?LOOP?inner_loop;???
????SET?i=i+1;???
????IF?i>12?THEN???
????????LEAVE?outer_loop;???
????END?IF;???
END?LOOP?outer_loop;??

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