MySQL provides us with a bunch of functions and operators that allow us to search JSON documents for various things, such as specific values, paths, keys, etc.
Here are seven functions and three operators that search JSON documents in MySQL.
Understanding the VAR_SAMP() Function in MySQL
In MySQL, the VAR_SAMP() function returns the sample variance of an expression. The denominator is the number of rows minus one.
If there are no matching rows, or if the expression is NULL, VAR_SAMP() returns NULL.
VAR_SAMP() is an aggregate function, and so it can be used with the GROUP BY clause.
The VAR_SAMP() function can also be used as a window function.
How VARIANCE() Works in MySQL
In MySQL, the VARIANCE() function returns the population standard variance of an expression.
If there are no matching rows, or if the expression is NULL, the function returns NULL.
The VARIANCE() function is a synonym for the standard SQL VAR_POP() function. In other words, they both do the same thing, but VARIANCE() is not standard SQL. Therefore, if you need to use standard SQL, use VAR_POP() instead.
Fix “WRONGTYPE Operation against a key holding the wrong kind of value” when using ZCOUNT in Redis
If you get an error that reads “WRONGTYPE Operation against a key holding the wrong kind of value” when using the ZCOUNT command in Redis, it’s probably because you’re passing a key with the wrong data type.
To fix this issue, be sure that the key you pass to the ZCOUNT command holds a sorted set.
Understanding the VAR_POP() Function in MySQL
In MySQL, the VAR_POP() function returns the population standard variance of an expression.
If there are no matching rows, or if the expression is NULL, VAR_POP() it returns NULL.
VAR_POP() is an aggregate function, and so it can be used with the GROUP BY clause.
The VAR_POP() function is standard SQL. There’s also a VARIANCE() function that does the same thing, but is not standard SQL.
Understanding the STDDEV_SAMP() Function in MySQL
In MySQL, the STDDEV_SAMP() function returns the sample standard deviation of a given expression. This is the square root of VAR_SAMP().
STDDEV_SAMP() is an aggregate function, and so it can be used with the GROUP BY clause.
If there are no matching rows, or if the expression is NULL, STDDEV_SAMP() returns NULL.
Overview of the STDDEV() Function in MySQL
In MySQL, the STDDEV() function returns the population standard deviation of a given expression.
STDDEV() is a synonym for the standard SQL function STDDEV_POP(). There’s also a STD() function which also does the same thing, so we can use either of these functions to get the same result.
Introduction to the STD() Function in MySQL
In MySQL, the STD() function returns the population standard deviation of a given expression.
STD() is a synonym for the standard SQL function STDDEV_POP(). There’s also a STDDEV() function which also does the same thing, so we can use either of these functions to get the same result.
Understanding the BIT_XOR() Function in MySQL
In MySQL, the BIT_XOR() function returns the bitwise XOR of all bits in a given expression.
XOR is an exclusive OR, and so a XOR b is mathematically equal to (a AND (NOT b)) OR ((NOT a) and b).