What is the method for SQL to find optimization
Today, the editor will share with you the relevant knowledge of what the SQL search optimization method is. The content is detailed and the logic is clear. I believe most people still know too much about this knowledge, so share this article for your reference. I hope you can get something after reading this article. Let's take a look at it.
The way most people write it at present
After several times of REVIEW code, such phenomena are found as follows:
In the business code, you need to query whether there are records based on one or more conditions, regardless of how many records there are. The common SQL and code writing methods are as follows
# SQL:
SELECT count (*) FROM table WHERE a = 1 AND b = 2
# Java:
Int nums = xxDao.countXxxxByXxx (params)
If (nums > 0) {
/ / execute the code here when it exists
} else {
/ / execute the code here when it does not exist
}
Does it feel very OK? there is no problem.
Optimization scheme
It is recommended to write as follows:
# SQL:
SELECT 1 FROM table WHERE a = 1 AND b = 2 LIMIT 1
# Java:
Integer exist = xxDao.existXxxxByXxx (params)
If (exist! = NULL) {
/ / execute the code here when it exists
} else {
/ / execute the code here when it does not exist
}
SQL no longer uses count, but uses LIMIT 1 instead, so that when a database query comes across, it will be returned, and do not continue to find how many entries are left.
Directly judge whether it is not empty in the business code.
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