More than one table query (can be linked with where)
En (intersection of multi-table queries)
Syntax :( link table left) inner join (link at right) on the condition (corresponding to the same table field)
Left link (left table of contents does not change, the corresponding table pairing)
Syntax :( links left table) left join (link at right) on the condition (corresponding to the same table field)
Right link (the right table of contents is not changed, the corresponding table pairing)
Syntax :( links left table) right join (link at right) on the condition (corresponding to the same table field)
2. Keyword Search
any some all
3. autocorrelation (equal to multi-table queries)
Attention to the need to modify the table name