![]() You cannot return a string in result_1 and an integer in result_2 and so on. The data-type of the results has to be uniform. But when you are using CASE in pair with a where clause, you need not to follow this (more on this later). Keep in mind that, the column must be present in the SELECT statement of your query, on which you are specifying the boolean expressions (in CASE). Conditional query constructs like the above are typically done with SELECT statements. In case, you don't specify the ELSE part the query will return null.Ī condition is generally applied on a column that is present in the table you are operating on. If all the expressions corresponding to WHEN are evaluated to be False, then the result respective to the ELSE part is shown. Here are some critical points that you should keep in mind while constructing CASEs in PostgreSQL:Įach condition is a boolean expression and based on its output the result is chosen. The following describes the general form of a PostgreSQL case with WHEN-THEN construct - CASE Let's now see the anatomy of a basic PostgreSQL CASE. You can explore the table with your own quick questions, and along the way, you may find out interesting facts. It turns out that there are 23 different regions covered in this table such as Western Europe, Polynesia, the Middle East and so on. SELECT COUNT(DISTINCT(region)) from countries How many regions exactly? The below query should give you the answer to the question. The table contains details about a total of 206 different countries from various regions of the world. ![]() ![]() Upon running a simple SELECT statement, you get to know about the columns, their data-types and also the rows the table is containing. Exploring the countries table very brieflyĪfter restoring the database, you can view the table in the pgAdmin interface which comes with the default installation of PostgreSQL. Let's now explore the countries table very briefly. You should have a table (populated with the details about different countries around the globe) by now if you restored the database backup. Also, you may want to form your own databases and tables. Feel free explore the tables provided in the database backup. This tutorial, however, only uses the countries table. After you successfully restore the backup, you should be able to see these tables in the database. If you want to know how to do this, you can follow this article. You can use this backup file and restore it in your PostgreSQL server. Intro to SQL for Data Science by DataCamp.Feel free to refresh the basics with the following resources: Note: To be able to follow along with this tutorial you need to know the basics of SQL and PostgreSQL. You will do this in the first section of this tutorial. In this tutorial, you will learn how to do this.īefore you start writing condition queries, it is important that you set up a local PostgreSQL database. You can formulate conditional expressions in PostgreSQL using WHEN-THEN case which is very similar to if-else blocks. Common conditional expressions include if-else blocks and switch cases. The differences between gin and gist will be explained in a future article.Conditional expressions are one of the most fundamental elements of any programming paradigm. Such indexes can be created as follows: CREATE INDEX gin_title ON book USING gin(title) ĬREATE INDEX gist_title ON book USING gist(title) The solution that we recommend is to create a gin or gist index. In PostgreSQL, the ILIKE operator can’t use a regular btree index. You simply avoid using wildcard characters: SELECT id FROM user WHERE name ILIKE 'john' Performance ILIKE can also be used as a case-insensitive equality operator. “Alice in Wonderland” has a capital A and a capital W, yet it will match this search. SELECT id FROM book WHERE title ILIKE 'alice%wonder%' Case-sensitive comparisonsĪll the following operators are case-sensitive: Making them case-insensitive requires the ILIKE operator and may require an additional index for performance reasons. In PostgreSQL, string comparisons are case-sensitive by default.
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