equi join

• 等值连接

  ej(leftTable, rightTable, matchingCols, [rightMatchingCols], [leftFilter], [rightFilter])

  兼容SQL的语法

  select * 
  from leftTable 
  [inner] join rightTable on t1.matchingCol=t2.rightMatchingCol 
  [where leftFilter and rightFilter]

• 有序等值连接：

  sej(leftTable, rightTable, matchingCols, [rightMatchingCols], [leftFilter], [rightFilter])

  兼容SQL的语法

  select * 
  from leftTable 
  [inner] join rightTable on leftTable.matchingCol=rightTable.rightMatchingCol 
  [where leftFilter and rightFilter] 
  order by matchingCol 

• leftTable 和 rightTable 是连接的表。

• matchingCols 是表示连接列的字符串标量或向量。

• rightMatchingCols 是表示右表连接列的字符串标量或向量。当 leftTable 和 rightTable 至少有一个连接列不同时，必须指定 rightMatchingCols。返回结果中的连接列与左表的连接列名称相同。

• leftFilter 和 rightFilter 条件表达式，作为左右表字段的过滤条件。多个条件之间用 and 或 or 连接。注意：若 leftTable / rightTable 指定为维度表或分区表，不支持指定 leftFilter, rightFilter。

返回与连接列匹配的行。有序等值连接 sej 的结果表会根据连接字段进行排序。

例1. 两个表等值连接，除了连接列外没有其他名称相同的列

t1= table(1 2 3 3 as id, 7.8 4.6 5.1 0.1 as value)
t2 = table(5 3 1 as id, 300 500 800 as qty);
t1;

t2;

ej(t1, t2,`id);

等价于

select * from t1 inner join t2 on t1.id=t2.id 

 ej(t2, t1,`id);

select * from t2 inner join t1 on t2.id=t1.id

ej(t1, t2,`id,, t1.id==3);

select * from t1 inner join t2 on t1.id=t2.id  where t1.id=3

例2. 等值连接两张表，它们含有相同名字的列，但是不以它作为连接列：

t1 = table(1 2 3 3 as id, 7.8 4.6 5.1 0.1 as value, 4 3 2 1 as x);
t1;

t2 = table(5 3 1 as id,  300 500 800 as qty, 44 66 88 as x) ;
t2;

select id, value, qty, x from ej(t1, t2, `id);

select id, value, qty, x from t1 inner join t2 on t1.id=t2.id

我们无需指定value和qty来自哪个表。系统首先会在左表中定位这两个列，如果左表没有这两个列，系统会在右表定位。

select id, value, qty, t2.x from ej(t1, t2, `id);

select id, value, qty, t2.x from t1 inner join t2 on t1.id=t2.id

ej(t1, t2, `id);

select * from t1 inner join t2 on t1.id=t2.id

ej选择了t1和t2中的两个x，然后将t2中的x重命名成t2_x。

例3. 多个连接列：

t1=table(1 1 2 2 3 3 as x, 1 2 2 3 3 4 as y, 1..6 as a);
t2=table(0 1 1 2 2 3 as x, 1 2 3 3 4 5 as y, 11..16 as b);
t1;

t2;

ej(t1, t2, `x`y);
// x, y是连接列

select * from t1 inner join t2 on t1.x=t2.x and t1.y=t2.y

t2.rename!(`x`y, `x2`y2);

ej(t1, t2, `x`y, `x2`y2);
// t1.x, t1.y t2.x2, t2.y2是连接列

select * from t1 inner join t2 on t1.x=t2.x2 and t1.y=t2.y2 

例4. 连接表时，可以使用表的别名：

table1=table(1 1 2 2 3 3 as x, 1 2 2 3 3 4 as y, 1..6 as a, 21..26 as c)
table2=table(0 1 1 2 2 3 as x, 1 2 3 3 4 5 as y, 4..9 as a, 11..16 as b);
select * from ej(table1 as t1, table2 as t2, `x`y) where t2.a<7;

在自连接时，必须使用表的别名：

t = table(`A`A`A`A`B`B`B`B as id, 1 3 6 9 1 9 12 17 as time, 1 2 6 3 5 9 4 0 as x)
select * from ej(t as a, t as b, `id) where a.time=b.time+3;

select * from t as a inner join t as b on a.id=b.id where a.time=b.time+3

例5. 指定 leftFilter 和 rightFilter

t1= table(1 2 3 3 as id1, 7.8 4.6 5.1 0.1 as value)
t2 = table(5 3 1 as id2, 300 500 800 as qty);
select * from ej(t1, t2, `id1, `id2, t1.value>1 and t1.value<6, t2.qty>300)

select * from t1 inner join t2 on t1.id1=t2.id2 where t1.value>1 and t1.value<6 and t2.qty>300