Tag: what is

Understanding the WINDOW Clause in MySQL

Posted on by Ian

In MySQL, the WINDOW clause is an optional clause that we can use to create a named window. The named window can then be referred to from a window function.

Many SQL developers define their window functions directly in the OVER clause. But that’s not the only way to do it. We can also define them in a WINDOW clause, and then refer to them in the OVER clause.

When we define the window function in a WINDOW clause, we name it. When we do this, we can refer to that name from the OVER clause. This eliminates the need to include the definition directly inside the OVER clause.

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Introduction to the OVER Clause in SQL

Posted on by Ian

When running SQL database queries, sometimes we need to use a window function in order to get the results we’re looking for. A window function is an aggregate-like function that enables partitioning and ordering of data within a result set.

The OVER clause is what enables us to create a window function.

The examples below demonstrate how we can incorporate the OVER clause in our SQL queries.

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Understanding the sys.quote_identifier() Function in MySQL

Posted on by Ian

In MySQL, we can use the sys.quote_identifier() function to quote a string to produce a result that can be used as an identifier in a SQL statement.

The string is returned enclosed by backticks (`), with each instance of a backtick doubled.

This function can be handy when a value to be used as an identifier is a reserved word or contains backtick characters.

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Understanding Window Functions in SQL

Posted on by Ian

Window functions can be a useful tool when writing SQL queries. They allow us to include aggregate data across multiple rows without getting those pesky errors that sometimes occur when we try to use an aggregate function in the wrong way.

In this article, I aim to provide a simple overview of window functions and how they can be used to provide a more useful result set when running SQL queries.

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Using the sys.format_statement() Function in MySQL to Truncate a SQL Statement

Posted on by Ian

In MySQL, the sys.format_statement() system function reduces the length of a given string/SQL statement to the length stored in the statement_truncate_len configuration option.

This function can be handy for truncating potentially long SQL statements retrieved from Performance Schema tables into a more suitable length (64 characters by default).

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Understanding the PS_THREAD_ID() Function in MySQL

Posted on by Ian

In MySQL, we can use the PS_THREAD_ID() function to get the Performance Schema thread ID assigned to a given connection ID. This can be useful whenever we use a function that takes the thread ID as its parameter, but we only know the connection ID.

If no thread ID exists for the connection, then NULL is returned.

The built-in PS_THREAD_ID() function does the same thing as the now deprecated sys.ps_thread_id() function. Therefore, we can call the function without needing to qualify it with sys or making sys our current schema.

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Understanding INFORMATION_SCHEMA in SQL

Posted on by Ian

Behind every well-structured and organised SQL database lies a treasure trove of information called metadata. Metadata is data that provides information about other data. In relational database management systems, this metadata can typically include information like the names of databases, tables, columns, the data type of a column, access privileges, and much more.

The SQL standard provides a collection of tables/views that allow us to view metadata about the objects in the database. The SQL standard refers to this as the information schema and calls it INFORMATION_SCHEMA.

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