We often hear terms like DDL, DML, DQL, and DCL when using relational database management systems (RDBMSs). But what exactly are they?
In this article we’ll look at what DML stands for, and what it does.
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What is DDL?
We often encounter terms like DDL, DML, DQL, DCL, and TCL when using relational database management systems (RDBMSs). But what do they mean?
In this article we’ll look at what DDL stands for and what it does.
How CONVERT() Works in MySQL
In MySQL, CONVERT() is a built in function that converts a value to another data type. It takes a value of one type and returns a value of the specified type.
We provide the value as an argument when we call the function, as well as the type that we want it converted to.
The CONVERT() function is similar to the CAST() function, which also converts between data types.
MySQL ROW_COUNT() Explained
In MySQL, ROW_COUNT() is a built-in function that returns the number of rows updated, inserted, or deleted by the preceding statement.
The value returned by ROW_COUNT() is often the same as the row count that the mysql client displays following statement execution, as well as the value from the mysql_affected_rows() C API function.
SQLite CHANGES() Function
The SQLite changes() function returns the number of database rows that were changed, inserted or deleted by the most recently completed INSERT, DELETE, or UPDATE statement, exclusive of statements in lower-level triggers.
Basically, it allows us to see how many rows are affected when we run any of those statements.
Signed vs Unsigned Integers
The integer data type is probably one of the more common data types when working with database management systems (and with computing in general). The integer is a numeric data type that allows us to store certain kinds of numbers.
More specifically, an integer is the number zero (0), a positive natural number (e.g. 1, 2, 3, …) or a negative integer with a minus sign (e.g. −1, −2, −3, …). Integers contain no decimal or fractional part.
However, many computing environments distinguish between signed integers and unsigned integers.
Let’s take a look at the difference between signed integers and unsigned integers.
FORMAT_BYTES() in MySQL
In MySQL, FORMAT_BYTES() is a built in function that converts a numeric byte count to a more human-readable format. It returns a string consisting of the value and a units indicator.
We provide the numeric byte count when we call the function.
SQLite ABS() Explained
In SQLite, ABS() is a built-in scalar function that returns the absolute value of its argument.
The absolute value is the non-negative equivalent of the argument. It can be thought of as the distance from zero that the number resides on the number line, without considering direction.
MySQL VERSION() Explained
In MySQL, VERSION() is a built-in function that returns the MySQL server version.
The result is a string that uses the utf8mb3 character set. A suffix may also be appended to the version number indicating server build or configuration information.
MySQL Date Format Specifiers (Full List)
The following table contains a full list of format specifiers that can be used in format strings with functions like DATE_FORMAT(), STR_TO_DATE(), and FROM_UNIXTIME() in MySQL.