Test Data Table:
suppliers 表
s_id s_name s_city s_zip s_call
------ -------------- --------- ------ --------
101 FastFruit Inc. Tianjin 300000 48075
102 LT Supplies Chongqing 400000 44333
103 ACME Shanghai 200000 90046
104 FNK Inc. Zhongshan 528437 11111
105 Good Set Taiyuang 030000 22222
106 Just Eat Ours Beijing 010 45678
107 DK Inc. Zhengzhou 450000 33332
fruits table
f_id s_id f_name f_price
------ ------ ---------- ---------
a1 101 apple 5.20
a2 103 apricot 2.20
b1 101 blackberry 10.20
b2 104 berry 7.60
b5 107 xxxx 3.60
bs1 102 orange 11.20
bs2 105 melon 8.20
c0 101 cherry 3.20
l2 104 lemon 6.40
m1 106 mango 15.60
m2 105 xbabay 2.60
m3 105 xxtt 11.60
o2 103 coconut 9.20
t1 102 banana 10.30
t2 102 grape 5.30
t4 107 xbababa 3.60
The first statement, do not understand, in the end is to return the query results information table, or ture
( presumably point: . The SELECT * the FROM suppliers the WHERE Fruits s_id. = Suppliers s_idthe AND fruits.s_id = 107` statement, fruits and suppliers formed a en )
SELECT * FROM fruits
WHERE EXISTS
(SELECT * FROM suppliers
WHERE fruits.`s_id` = suppliers.`s_id` AND fruits.s_id=107);
f_id s_id f_name f_price
------ ------ ------- ---------
b5 107 xxxx 3.60
t4 107 xbababa 3.60
The following results of a query in the two tables:
SELECT * FROM suppliers ,fruits
WHERE fruits.`s_id` = suppliers.`s_id` AND fruits.s_id=107
s_id s_name s_city s_zip s_call f_id s_id f_name f_price
------ ------- --------- ------ ------ ------ ------ ------- ---------
107 DK Inc. Zhengzhou 450000 33332 b5 107 xxxx 3.60
107 DK Inc. Zhengzhou 450000 33332 t4 107 xbababa 3.60
The second statement, then the query returns ture, and then query the entire data table fruits
(guess points: the SELECT * Suppliers the WHERE s_id = the FROM statement Suppliers table 107 and the upper layer is not connected condition SELECT fruits )
SELECT * FROM fruits
WHERE EXISTS
(SELECT * FROM suppliers WHERE s_id=107);
f_id s_id f_name f_price
------ ------ ---------- ---------
a1 101 apple 5.20
a2 103 apricot 2.20
b1 101 blackberry 10.20
b2 104 berry 7.60
b5 107 xxxx 3.60
bs1 102 orange 11.20
bs2 105 melon 8.20
c0 101 cherry 3.20
l2 104 lemon 6.40
m1 106 mango 15.60
m2 105 xbabay 2.60
m3 105 xxtt 11.60
o2 103 coconut 9.20
t1 102 banana 10.30
t2 102 grape 5.30
t4 107 xbababa 3.60
