left join (left join) returns all records in the left table and records with equal join fields in the right table
right join (right join) returns including the right table All records in the left table with equal join fields
inner join (equi-join) returns only records with equal join fields in both tables
2. Modify a field in the data in the table
update table_name set column1 = value1, colunm2 = value2...where ...;
3. Add or modify fields to the table
ALTER TABLE table_name ADD/MODIFY columnName type (int) default value (DEFAULT NULL) description (COMMENT)
Fourth, case when syntax
There are two forms
1. column is any field that needs to be compared, value is the value to compare, result is the specified result, and name is the column name that returns this column
CASE column WHEN value1 THEN result1 WHEN value2 THEN result2 ... ELSE result3
END AS NAME
2, the two spellings are basically similar
CASE
WHEN column = value1 THEN result1
WHEN column = value2 THEN result2 ...
ELSE result3
END AS NAME
practise
SELECT login_name ,
CASE login_name
WHEN 'dawn' THEN 'star'
WHEN 'lisi' THEN 'ordinary man'
ELSE 'not a man'
END AS type
FROM saut_m_user WHERE id > 0
result
5. Pass in an array parameter in mapper
<if test="applyStatus != null and applyStatus.size() > 0 ">
and loan.apply_status in
<foreach item="item" index="index" collection="applyStatus"
open="(" separator="," close=")">
#{item, jdbcType=BIGINT}
</foreach>
</if>