我有三个表

table1                     table2                    table3

col1                        col3  col4                   col5    col6

a                             a        5                       a       6

b                             c        7                       b       2

c                             d        9                       d       3

d

想用select生成一表如下：

col1    col4    col6

a         5          6

b          0         2

c         7          0

d          9         3