Mysql中查询(数据库中的)纵向转(查询结果显示为)横向.

1、在mysql环境，创建数据库表，

create table test_data1(id int, name VARCHAR(20), day VARCHAR(20))

2、插入测试数据，

insert into test_data1 values(1,'liu',1)

insert into test_data1 values(2,'liu',3)

insert into test_data1 values(3,'wang',1)

insert into test_data1 values(4,'wang',2)

insert into test_data1 values(4,'wang',4)

3、查询表中数据，select * from test_data1；

4、编写目标sql；

select name, 

     max(case when day=1 then 1 end) d_1,

     max(case when day=2 then 2 end) d_2,

     max(case when day=3 then 3 end) d_3,

     max(case when day=4 then 4 end) d_4

from test_data1 t group by name

这是最典型的自关联，应该是这样的：

SELECT a.user_id, a.content, b.content, c.content, d.content,

e.content, f.content, g.content, h.content, i.content

FROM sj_reg_extend_info a,

sj_reg_extend_info b,

sj_reg_extend_info c,

sj_reg_extend_info d,

sj_reg_extend_info e,

sj_reg_extend_info f,

sj_reg_extend_info g,

sj_reg_extend_info h,

sj_reg_extend_info i

WHERE a.reg_field_id=1

AND b.reg_field_id=6 AND b.user_id=a.user_id

AND c.reg_field_id=9 AND c.user_id=a.user_id

AND d.reg_field_id=10 AND d.user_id=a.user_id

AND e.reg_field_id=11 AND e.user_id=a.user_id

AND f.reg_field_id=4 AND f.user_id=a.user_id

AND g.reg_field_id=5 AND g.user_id=a.user_id

AND h.reg_field_id=7 AND h.user_id=a.user_id

AND i.reg_field_id=8 AND i.user_id=a.user_id

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