Table used herein:

 	Table SC
+------+-------+
| sid  | score |
+------+-------+
| 01   |  80.0 |
| 01   |  90.0 |
| 01   |  99.0 |
| 02   |  70.0 |
| 02   |  60.0 |
| 02   |  80.0 |
| 03   |  80.0 |
| 03   |  80.0 |
| 03   |  80.0 |
+------+-------+

group by

SQL often appears below

ERROR 1140 (42000): In aggregated query without GROUP BY

First explain

AggRegate is a kind of function in SQL, which is calledPolymerization function, The following is a polymeric function

• AVG () - Return the average
• Count () - Return to the number of rows
• First () - Returns the value of the first record
• Last () - Returns the value of the last record
• Max () - Return to the maximum
• MIN () - Return minimum
• SUM () - Return to sum

So this error is that you wrote a query statement containing the aggregate function but does not use the group BY group.

So why didn't you use the group by grouping?

Take the SUM function in the polymerization function as an example. SUM (score) calculates the sum column, if SID and SUM (SCORE) are selected at the same time in the SQL query statement

select sid,sum(score) from sc;

Imagine what results will be returned on the above statement? Is there a strong relationship between two columns in the result of the return?

Obviously such query statements are unknown, so there is a reasonable table that cannot be returned.

In order to make the return result reasonable, the meaning of the query statement will be further clarified.

So you need to use Group By to modify the above query statement.

The literal meaning of Group By is "packet", transfer the door in SQL to modify the aggregate function

select sid,sum(score) from sc
group by sid;

The above SQL statement means that SID is based on the basis for packets, and SCORE is subjected to summing. The SUM that has been obtained is correct with the SID. In this case, the meaning is the total division of each SID.

When the SQL query statement has selected multiple fields in addition to the aggregate function, add the relationship between group by, the truth is simple, if one of the various fields is the basis for the group, then the remaining fields It is not possible to make a clear and reasonable association with the polymerization function.

At lastBy modifying the SQL_MODE variable, it can make the polymer function to force the binding group by Return the result, the modification is as follows.

set sql_mode ='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';