Mysql substr() function
Содержание:
How Can I Use Oracle SUBSTR To Remove the Last Character?
The best way to use Oracle SUBSTR to remove last character is using a combination of SUBSTR and LENGTH.
The LENGTH function can be used to determine the length parameter of the function. Remember, functions can contain other functions as parameters.
This function would be:
In this case, n can be set to 1 as you want to remove the last character. It can be set to another value if you want more characters removed.
For example, to remove the last character from the name of this site, “Complete IT Professional”, the function would be:
This would return:
“Complete IT Professiona”
See the Examples section below for more examples.
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Example
Let’s look at some Oracle CONCAT function examples and explore how to use the CONCAT function in Oracle/PLSQL.
For example:
CONCAT('Tech on', ' the Net') Result: 'Tech on the Net' CONCAT('a', 'b') Result: 'ab'
Concatenate More Than 2 Values
In Oracle, the CONCAT function will only allow you to concatenate two values together. If you want to concatenate more values than two, you can nest multiple CONCAT function calls.
For example:
SELECT CONCAT(CONCAT('A', 'B'),'C') FROM dual; Result: 'ABC'
This example would concatenate the 3 values together and return ‘ABC’.
To concatenate 4 values, you can nest one more CONCAT function call.
For example:
SELECT CONCAT(CONCAT(CONCAT('A', 'B'),'C'),'D') FROM dual; Result: 'ABCD'
This example would concatenate the 4 values together and return ‘ABCD’.
Concatenate Single Quotes
Since the parameters within the CONCAT function are separated by single quotes, it isn’t straight forward how to add a single quote character within the result of the CONCAT function.
Let’s look at a fairly easy example that shows how to add a single quote to the resulting string using the CONCAT function.
For example:
SELECT CONCAT('Let''s', ' learn Oracle') FROM dual; Result: Let's learn Oracle
Example — Match on Digit Characters
Let’s look next at how we would use the REGEXP_SUBSTR function to match on a single digit character pattern.
For example:
SELECT REGEXP_SUBSTR ('2, 5, and 10 are numbers in this example', '\d') FROM dual; Result: 2
This example will extract the first numeric digit from the string as specified by . In this case, it will match on the number 2.
We could change our pattern to search for a two-digit number.
For example:
SELECT REGEXP_SUBSTR ('2, 5, and 10 are numbers in this example', '(\d)(\d)') FROM dual; Result: 10
This example will extract a number that has two digits side-by-side as specified by . In this case, it will skip over the 2 and 5 numeric values and return 10.
Now, let’s look how we would use the REGEXP_SUBSTR function with a table column and search for a two digit number.
For example:
SELECT REGEXP_SUBSTR (address, '(\d)(\d)') FROM contacts;
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Practice Exercise #2:
Based on the employees table populated with the following data, find all records whose employee_name contains the letter «s».
CREATE TABLE employees ( employee_number number(10) not null, employee_name varchar2(50) not null, salary number(6), CONSTRAINT employees_pk PRIMARY KEY (employee_number) ); INSERT INTO employees (employee_number, employee_name, salary) VALUES (1001, 'John Smith', 62000); INSERT INTO employees (employee_number, employee_name, salary) VALUES (1002, 'Jane Anderson', 57500); INSERT INTO employees (employee_number, employee_name, salary) VALUES (1003, 'Brad Everest', 71000); INSERT INTO employees (employee_number, employee_name, salary) VALUES (1004, 'Jack Horvath', 42000);
Solution for Practice Exercise #2:
The following Oracle SELECT statement would use the Oracle LIKE condition to return the records whose employee_name contains the letter «s».
SELECT * FROM employees WHERE employee_name LIKE '%s%';
It would return the following result set:
EMPLOYEE_NUMBER | EMPLOYEE_NAME | SALARY |
---|---|---|
1002 | Jane Anderson | 57500 |
1003 | Brad Everest | 71000 |
Example — Using Escape Characters
It is important to understand how to «Escape Characters» when pattern matching. These examples deal specifically with escaping characters in Oracle.
Let’s say you wanted to search for a % or a _ character in the Oracle LIKE condition. You can do this using an Escape character.
Please note that you can only define an escape character as a single character (length of 1).
For example:
SELECT * FROM suppliers WHERE supplier_name LIKE 'Water!%' ESCAPE '!';
This Oracle LIKE condition example identifies the ! character as an escape character. This statement will return all suppliers whose name is Water%.
Here is another more complicated example using escape characters in the Oracle LIKE condition.
SELECT * FROM suppliers WHERE supplier_name LIKE 'H%!%' ESCAPE '!';
This Oracle LIKE condition example returns all suppliers whose name starts with H and ends in %. For example, it would return a value such as ‘Hello%’.
You can also use the escape character with the _ character in the Oracle LIKE condition.
For example:
SELECT * FROM suppliers WHERE supplier_name LIKE 'H%!_' ESCAPE '!';
Parameter Values
Parameter | Description |
---|---|
string | Required. Specifies the string to return a part of |
start | Required. Specifies where to start in the string
|
length | Optional. Specifies the length of the returned string. Default is to the end of the string.
|
Practice Exercise #2:
Based on the contacts table, delete all records from the contacts table whose contact_id is greater than or equal to 5000 and less than 6000.
CREATE TABLE contacts ( contact_id number(10) not null, last_name varchar2(50) not null, first_name varchar2(50) not null, address varchar2(50), city varchar2(50), state varchar2(2), zip_code varchar2(10), CONSTRAINT contacts_pk PRIMARY KEY (contact_id) );
Solution for Practice Exercise #2:
The following Oracle DELETE statement would delete these records from the contacts table:
DELETE FROM contacts WHERE contact_id >= 5000 AND contact_id < 6000.
Or you could write the solution using the BETWEEN clause as follows:
DELETE FROM contacts WHERE contact_id BETWEEN 5000 AND 5999;
Frequently Asked Questions
Question: How can you use the CONCAT function to concatenate more than 2 strings together?
Answer: Since the CONCAT function will only let you concatenate 2 strings, you will need to nest multiple CONCAT functions to concatenate more than 2 strings together.
For example, to concatenate 3 strings, you could nest the CONCAT function as follows:
CONCAT( CONCAT( string1, string2 ), string3 )
Or you could nest the CONCAT function as follows, if you wanted to concatenate 4 strings:
CONCAT( CONCAT( CONCAT( string1, string2 ), string3 ), string4 )
Here is an example provided by Ruth that demonstrates how to nest multiple CONCAT functions to concatenate 6 strings:
CONCAT( CONCAT( CONCAT( CONCAT( CONCAT( 'I like ', t.type_desc_column), ' cake with '), t.icing_desc_column),' and a '), t.fruit_desc_column)
The CONCAT function is one method to concatenate strings in Oracle. An alternative to using the CONCAT function would be to use the || operator to catenatenate multiple strings, as follows:
'I like ' || t.type_desc_column || ' cake with ' || t.icing_desc_column || ' and a ' || t.fruit_desc_column
Practice Exercise #1:
Based on the contacts table, delete all records from the contacts table who reside in the City of ‘Las Vegas’ and whose first_name is ‘Jane’.
CREATE TABLE contacts ( contact_id number(10) not null, last_name varchar2(50) not null, first_name varchar2(50) not null, address varchar2(50), city varchar2(50), state varchar2(2), zip_code varchar2(10), CONSTRAINT contacts_pk PRIMARY KEY (contact_id) );
Solution for Practice Exercise #1:
The following Oracle DELETE statement would delete these records from the contacts table:
DELETE FROM contacts WHERE city = 'Las Vegas' AND first_name = 'Jane';