How optimize MySQL query with multiple joins?
- Check if you really have to select every column in all of the tables?
- You may also want to consider reducing the load on the database by using caching applications like sphinxsearch and memcached.
- Check none of your joins are to views rather than actual tables.
How can I make MySQL query execution faster?
Let’s have a look at the most important and useful tips to improve MySQL Query for speed and performance.
- Optimize Your Database.
- Optimize Joins.
- Index All Columns Used in ‘where’, ‘order by’, and ‘group by’ Clauses.
- Use Full-Text Searches.
- MySQL Query Caching.
Why SQL count is slow?
Counting tables with large amount of data may be very slow, sometimes it takes minutes; it also may generate deadlock on a busy server.
What is the difference between count 1 and count (*) in a SQL query?
The difference is simple: COUNT(*) counts the number of rows produced by the query, whereas COUNT(1) counts the number of 1 values. If you use COUNT(column), the database must actually inspect the individual values in the column, since it will not count NULLs. Aggregate functions like COUNT and SUM always ignore NULLs.
Why count 1 is faster than count (*)?
Count(*) or Count(1) that is the question. According to this theory COUNT(*) takes all columns to count rows and COUNT(1) counts using the first column: Primary Key. Thanks to that COUNT(1) is able to use index to count rows and it’s much faster.
What is the difference between Count and Count * Function?
The COUNTA is basically a cousin function of COUNT. While COUNT tallies the cells that contain only the numeric values, COUNTA counts all the non-blank cells, regardless of the data types the cells use – it could be numbers, Boolean values, text, logical values, empty strings, and even error values.
What is difference between Counta and Countblank?
COUNT counts how many cells in a range contain numeric data (numbers). COUNTA counts how many populated cells in a range (i.e. not blank). COUNTBLANK counts how many blank cells in a range.
What’s the difference between Countif and Countifs?
The difference is that COUNTIF is designed for counting cells with a single condition in one range, whereas COUNTIFS can evaluate different criteria in the same or in different ranges.
How do I use count and Counta in Excel?
COUNT function counts cells that contain only numbers, but COUNTA function counts cells that are not blank, including numbers. As Date and Time values are stored as serial numbers in Excel so these values are counted in both of these functions.
Can I use Counta and Countif together?
We can use a combination of the COUNTA, COUNTIF, and SUMPRODUCT functions to get the desired results. We can list down the things we wish to exclude from counting. One other way to arrive at the same result is to use the formula =COUNTIFS(B4:B9,”<>Rose”B4:B9,”<>Marigold”).
What is the difference between count () and count (*) function?
Difference between count(*) and count(columnName) in MySQL? The count(*) returns all rows whether column contains null value or not while count(columnName) returns the number of rows except null rows. Let us first create a table.
What’s the difference between count and count distinct?
Count would show a result of all records while count distinct will result in showing only distinct count. For instance, a table has 5 records as a,a,b,b,c then Count is 5 while Count distinct is 3.
What does count (*) do in SQL?
COUNT(*) returns the number of rows in a specified table, and it preserves duplicate rows. It counts each row separately. This includes rows that contain null values.
Which is better count (*) or Count 1?
The simple answer is no – there is no difference at all. The COUNT(*) function counts the total rows in the table, including the NULL values. The semantics for COUNT(1) differ slightly; we’ll discuss them later. However, the results for COUNT(*) and COUNT(1) are identical.
How do I count rows in SQL query?
To counts all of the rows in a table, whether they contain NULL values or not, use COUNT(*). That form of the COUNT() function basically returns the number of rows in a result set returned by a SELECT statement.
How do I count the number of rows in SQL without counting?
Count Rows of a table Without using Count() Function
- SELECT so.[name] as.
- , CASE WHEN si. indid between 1 and 254.
- THEN si.[name] ELSE NULL END.
- AS [Index Name]
- , si. indid, rows.
- FROM sys. sysindexes si.
- INNER JOIN sysobjects so.
- ON si. id = so. id.
How do I count the number of rows with the same value in SQL?
How to Find Duplicate Values in SQL
- Using the GROUP BY clause to group all rows by the target column(s) – i.e. the column(s) you want to check for duplicate values on.
- Using the COUNT function in the HAVING clause to check if any of the groups have more than 1 entry; those would be the duplicate values.
Can we use count in where clause?
SQL SELECT COUNT with WHERE clause SQL SELECT COUNT() can be clubbed with SQL WHERE clause. Using the WHERE clause, we have access to restrict the data to be fed to the COUNT() function and SELECT statement through a condition.
How do I count the number of rows with the same value in mysql?
Find duplicate values in one column
- First, use the GROUP BY clause to group all rows by the target column, which is the column that you want to check duplicate.
- Then, use the COUNT() function in the HAVING clause to check if any group have more than 1 element. These groups are duplicate.
How do I count occurrences in mysql?
“mysql count number of occurrences in a column” Code Answer
- SELECT name,COUNT(*)
- FROM tablename.
- GROUP BY name.
- ORDER BY COUNT(*) DESC;
How do I count the number of unique values in a column in MySQL?
Distinct Counts The COUNT(DISTINCT) function returns the number of rows with unique non-NULL values. Hence, the inclusion of the DISTINCT keyword eliminates duplicate rows from the count. Its syntax is: COUNT(DISTINCT expr,[expr…])