Problem recording and thinking

Preface ： Daily problem recording and thinking .

Mysql Group by sentence

Study group by The first thing to know is What are aggregate functions ？ What are the aggregation functions ？

mysql8.0 Aggregate function

Most common usage , Check the minimum specifications for each product .

SELECT
	goods_id,
	min( goods_price ) 
FROM
	tb_sku_info 
GROUP BY
	goods_id

But we may need other fields such as id perhaps name wait , An error may be reported when querying non aggregated columns , For example, the following statement .

SELECT
	id,
	goods_id,
	min( goods_price ) 
FROM
	tb_sku_info 
GROUP BY
	goods_id

Inquire about sql_mode sentence

select @@sql_mode

set @@sql_mode = ONLY_FULL_GROUP_BY

select * from config_info group by group_id

1055 - Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 
'nacos_config.config_info.id' which is not functionally dependent on columns in GROUP BY clause; 
this is incompatible with sql_mode=only_full_group_by

Remove sql_mode in ONLY_FULL_GROUP_BY This specification is incorrect , If you don't pay attention, it will cause other problems .

The most obvious is Wrong line problem .

SELECT
	id,
	specifications,
	goods_id,
	min( goods_price ) 
FROM
	tb_sku_info 	
GROUP BY
	goods_id

The query results are shown in the figure

After querying the general table, you can see that the price in the red box is the lowest price of goods .

Correct writing , Query through a link , use The lowest price is id Two Field to uniquely match row records in the main table .

SELECT
	* 
FROM
	tb_sku_info AS t1
	INNER JOIN ( SELECT goods_id, min( goods_price ) AS mixPrice FROM tb_sku_info GROUP BY goods_id ) AS t2 ON t1.goods_id = t2.goods_id 
	AND t1.goods_price = t2.mixPrice