Question

我有两张看起来像这样的表：

带有字段的检查点：

  Checkpoint_id
  Checkpoint_name

checkpoint_id是主键

Checkpoint_data包含字段：

Checkpoint_id
sequence_number
data

（checkpoint_id，sequence_number）是主键

我想要做的是获取checkpoint_id及其名称，还总结通过checkpoint_id链接的所有数据的长度。例如，我想获得sequence_number 1,2,3和4的长度，然后将所有数据的长度相加，并返回相应的检查点ID和名称。数据字段是varchar

Answer 1

SELECT c.checkpoint_id, c.checkpoint_name, sum(length(cd.data))
FROM checkpoint c 
INNER JOIN checkpoint_data cd ON c.checkpoint_id = cd.checkpoint_id
GROUP BY c.checkpoint_id

编辑：

SELECT c.checkpoint_id, c.checkpoint_name, sum(length(cd.data))
FROM checkpoint c 
INNER JOIN checkpoint_data cd ON c.checkpoint_id = cd.checkpoint_id
GROUP BY c.checkpoint_id, c.checkpoint_name

Answer 2

有两列：first_name，last_name into table employees。

SELECT first_name,
       last_name,
       LENGTH(first_name)+LENGTH(last_name) 
           as "Length of name" FROM employees;

总结varchar的长度

2 个答案: