SQL, the wildcard characters of the LIKE operator (%, _ , [] and ^)

Hi Guys,

Today a quick and easy post to answer a question that was asked to me some time ago.


We will talk about the wildcard characters of the like operator.
In its simplicity I think it is useful to who is entering the world of the SQL language.

Enjoy the reading!



Wildcard characters of the LIKE operator

SQL ANSI LIKE operator has different wildcard characters which are:
  • The percent sign %
  • The underscore _
  • The square braket [^] and []
 
Their use is very simple!
 
 
The percent sign (%) wildcard

The percent sign (%) allows you to find if a substring is contained within a string.
 
For example we can write the following query:

SELECT * FROM ITEMS WHERE NAME LIKE '%AD%'
This statements will return all the rows of items table where the field name contain the string "AD" in any position. 
For example:
 
RADIO
BLADE
ADVERTISING


The underscore ( _ ) wildcard

Looking at the following statement the underscore wildcard allows you to find all the rows of the table items where the field name contain the substring "R_CE" where the "_" can be any single character

SELECT * FROM ITEMS WHERE NAME LIKE '%R_CE%'
For example:

RACE
RICE


The bracket square [] and [^] wildcard

Looking at the following statement the bracket square allow you to find all the rows of the table items where the field name contain the substring "R*CE" where * can be only the character "A" or "B".

SELECT * FROM ITEMS WHERE NAME LIKE '%R[AB]CE%'
 
What is contained within the square brackets are characters that you are trying to match on.
So in the following statement we are search the field name for the presence of a substring "R*CE" where * can be a character from A to F.

SELECT * FROM ITEMS WHERE NAME LIKE '%R[A-F]CE%'
  
The character ^ simply means not within.




That'all for today!
Luca
 
Follow me on linkedin if you like theese posts!












Comments

Post a Comment

I Post più popolari

SQL Server, execution plan and the lazy spool (clearly explained)

Image
Hi Guys, Welcome back! In one of the last posts we talked about Table Spool . We had explained what Spool are for by telling the somewhat curious story of the halloween problem . Here we specifically talked about a type of spool called Eager Spool   You can look to the execution plan below where the eager Spool is used to avoid the halloween problem in classic query of the "salary increase".. i suggest Well, if the story of the eager spool intrigued you, today instead we will speak about another type of Spool, the Lazy Spool . The Lazy spool Let's take a small step back. So, what is a Spool operation?  As we have already understood a spool operation is simply a temporary storage of data . Data are read from a source table and stored inside a worktable in the Tempdb database . While an Eager Spool is used to prevent the Halloween problem, the Lazy Spool is instead used to store data that will later be needed again when running a query . So, when a Lazy spool is used?  ...
Read more

SQL Server, datetime vs. datetime2

Image
Hi guys, This time, in this post we will speak about datetime and datetime2 datatypes. We will talk about the pros and cons. We will talk about all the differences between the two types of data. Write me in the comments which type of data do you prefer between the two. Enjoy the reading!     Datetime Vs. Datetime2 First of all, it must be said that the datatype datetime is certainly the best known native format for storing a date in SQL Server. However, Microsoft has also been introducing a new type of data for many years now, also used to manage dates. It is in fact from SQL server 2008 that it is present in datetime2 data type. This "new" type of data was born primarily to have higher accuracy . Let's in fact talk about ... precision ! Datetime Certainly the datetime data type is not very precise and certainly there are many cases in which its precision is simply not sufficient. Let's see it with an example. Open the SQL Management studio (SSMS) and write the fo...
Read more

La clausola NOLOCK. Approfondiamo e facciamo chiarezza!

Image
Ehi ragazzi! La domanda è di quelle importanti! Siete pronti per scoprire tutto ma proprio tutto sulla clausola NOLOCK?   Se la riposta è si, allora seguitemi! Oggi ne spiegheremo il funzionamento in maniera approfondita. Faremo una introduzione al concetto di tipi di LOCK Ed infine vedremo come mai una SELECT ne può bloccare un'altra. Non vi nascondo che il motivo di questo articolo è fare chiarezza. Su questo argomento si sentono spesso affermazioni “curiose” ma tra le tante questa è la prima: “ uso la SELECT con l’opzione WITH(LOCK) così non blocco le altre tabelle ”.   Ma, è proprio vero quanto affermato? Beh oggi facciamo il punto!   Buona lettura!     La clausola NOLOCK Diciamo subito per iniziare che cos’è la NOLOCK. NOLOCK è il nome di una clausola che è possibile specificare all’interno di uno statement di tipo SELECT utilizzando la seguente sintassi: SELECT * FROM TABELLA WITH (NOLOCK) Si noti che non possiamo ...
Read more