select id, (select sum ( test_field ) from test2 where test_id = test2_id) as total from test order by total limit 5
does a sql like this cause slowness? is there any solution
select id, (select sum ( test_field ) from test2 where test_id = test2_id) as total from test order by total limit 5
does a sql like this cause slowness? is there any solution
you have only one piece of data in this query. Why do you still use subqueries and order by??
well, that's all I can write.
use JOIN
$selectTip = $pdo->query("SELECT * FROM `tips_rate` WHERE `tip_id` = ".$row[ id ]." " ); $selecttotal = mysqli_num_rows($selectTip); $rate = $pdo->query("SELEC...
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subject table, which can be understood as a classification table. The course and source_book tables are associated with subject now use the subject table as the main table to query how many courses and books are under this category. query statemen...
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as shown in the following figure the current time is 16 41 00. I want to take this section of data every two hours. How should sql write ? ...
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I want to optimize a sentence about group by. I don t know where to start. I want to find a train of thought . SELECT adv_id, network_id, SUM(re_click) AS clk, SUM(deny_click) AS dny_clk, SUM(re_conver) AS re_ins, SUM(mat_conver) AS mat_ins, SUM(def_...
background: 1. I am a java programmer 2. Recently interviewed for a senior development position 3. The previous project mainly used less oracle,mysql, and the companies interviewed basically used mysql s 4. I am weak in the database 5. Recently, I...
like this SELECT * FROM material WHERE {key:value} limit 1 ...
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Table structure ...
use mybatis to configure custom secondary cache. Using xml annotation can use < cache type= "com.test.dao.MybatisRedisCache " > to successfully use custom cache, but using @ CacheNamespace (implementation = MybatisRedisCache.class) on the dao i...
class essay extends Model { public function comment() { return $this->hasMany( App comment ) } } class comment extends Model { public function essay() { return $this->belongsTo( App essay ) } } ...
mybatis+mysql for java projects int batchAmount = 20000; for (int startIndex = 0; startIndex < size; startIndex += batchAmount) { int endIndex = startIndex + batchAmount; endIndex = (endIndex &...
Master and Slave built by mysql5.6, the newly created table is not backed up to the slave library master and slvae data can both correspond to can t the test library be automatically backed up to the slave library when establishing a master-slav...
I want to do a circular sequence to output pictures. Don t know how to write this code? Table structure for example, now the field ID of key=1 is 1, 2, 5, 7, 10, 11, 6 fields I want to output one at a time in order. output id 1 field for t...
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ask God to help me translate this native SQL statement into TP5 thank you! It is Db:: ( name )-> this kind of chained operation select a.id, a.titlerect a. Createwriting time as answer_count from fa_question a. Isometric solvepaper count (b.qid) as ...