LINQ To SQL

https://www.got-it.ai/solutions/sqlquerychat/sql-help/data-query/linq-to-sql-join-table-examples-c-querychat/

INNER JOIN 多条件匹配

var query =
    from t1 in myTABLE1List // List<TABLE_1>
    join t2 in myTABLE1List
      on new { A = t1.ColumnA, B = t1.ColumnB } equals new { A = t2.ColumnA, B = t2.ColumnB }
    join t3 in myTABLE1List
      on new { A = t2.ColumnA, B =  t2.ColumnB } equals new { A = t3.ColumnA, B = t3.ColumnB }
    ...

LEFT OUTER JOIN

var query =
    from t1 in myTABLE1List // List<TABLE_1>
    join t2 in myTABLE1List 
    on new { A = t1.ColumnA, B = t1.ColumnB } equals new { A = t2.ColumnA, B = t2.ColumnB }
    into temp from t3 in temp.DefaultIfEmpty()
    ...

RIGHT OUTER JOIN

var query =
    join t2 in myTABLE1List 
    from t1 in myTABLE1List // List<TABLE_1>
    on new { A = t2.ColumnA, B = t2.ColumnB } equals new { A = t1.ColumnA, B = t1.ColumnB }
    into temp from t3 in temp.DefaultIfEmpty()
    ...