![]() To name a few use cases, you can do the following: Getting PostgreSQL metadata can help you have information about databases, tables, schema, indexes, columns, functions, and even size information. This is useful, especially if the record length is long. One pro tip on CoderPad sandbox is to head over to the right terminal and run this to prettify the output of the SQL command: You can also use CoderPad’s sandbox, which uses PostgreSQL 12. Getting started: Prerequisitiesįollowing this tutorial, you’ll need to write SQL commands in your desired SQL client. Each column starts with “con” except for the oid column, which is the row identifier. These kinds of objects are referred to as “relations”.Ī typical example is a pg_constraint catalog, which stores primary, unique, and foreign keys and table constraints. This is because the pg_class catalog stores all information about tables and other objects that have columns. pg_namespace, which has columns that begin with “nsp”.Īnother interesting example is pg_class, which has columns that start with “rel”.pg_proc, which has columns that start with “pro”.For example, the pg_database has columns starting with “dat”, like datname, which is the database name column. A high percentage of columns – if not all – have a prefix of a combination of three letters of the name after “pg_”. PostgreSQL has some funny naming conventions for the column names of system catalogs. However, most system catalogs are database-specific.Įach system catalog name starts with “pg_”. So you shouldn’t change the system catalogs unless you really know what you’re doing.Ī few system catalogs are shared across all databases in the PostgreSQL cluster. You can insert new rows, update values, add columns – or potentially mess up your system. These catalogs are regular tables where you can manipulate data as you do with other tables. System catalogs are where a database management system stores schema metadata, such as information about databases, tables, and columns. Each catalog is a collection of schemas, and each schema has a set of tables. When you set up PostgreSQL in your machine, you spin up a PostgreSQL cluster, a server that hosts databases. This tutorial aims to give you insights into how PostgreSQL system catalogs can help you manage your schemas, databases, tables, and even table columns. In this tutorial, you’ll learn about the internal building blocks of PostgreSQL – also known as system catalogs – to see how the PostgreSQL backend is structured. Using this method we will select the fields we want directly from the pg_user table.PostgreSQL is a well-known database engine that allows you to write performant SQL queries. ![]() There is another way to achieve the same result using SQL. Note that this may be different on your computer. We get an output username and user_attribute with a user named postgres who has the attribute "superuser". Line 9: Lastly, we order the result in ascending order. Line 8: We'll fetch all the results from the pg_user table which gives us access to information about database users. Line 7: We commit this transaction using the END keyword. Line 4: We print out the "superuser" using CAST here because we have to perform a conversion between two data types. Line 3: The usesuper is a boolean type for a "superuser", so what we are saying here is that if the user is a "superuser", perform the operations on lines 4 and 6. ![]() Line 2: We introduced the CASE expression, which is the same as the if/else statement in most programming languages. Line 1: We select the usename using an alias username.
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