资讯

I have three tables. Table 1 has 1 record, and joins to Table 2 on an field called ID which has 5 records. Table 2 joins to Table 3, which has 1 record. The only reason I'm linking in table 2 is ...
Read this SQL tutorial to learn when to use SELECT, JOIN, subselects and UNION to access multiple tables with a single statement.
In a three-way join, the sql-expression consists of two conditions: one relates the first table to the second table and the other relates the second table to the third table.