Here's an example of the REPLACE() function that changes the protocol of a URL from "http" to "https": Let's Get Countingīy combining LENGTH() and REPLACE() with the ROUND() function, we can obtain a count of a specific sub-string in a field that contains textual content. To count straight characters, use CHAR_LENGTH() instead. This has some important ramifications because it means that for a string containing five 2-byte characters, LENGTH() returns 10. The LENGTH() function returns the length of a string in bytes. LENGTH() returns the length of a string in bytes REPLACE() returns the string str with all occurrences of the string from_str replaced by the string to_str, by performing case-sensitive matching. The two functions that we'll be using here today are LENGTH(str) and REPLACE(str, from_str, to_str). Introducing the LENGTH() and REPLACE() Functions In today's blog, we'll learn how to count the number of string occurrences within a char, varchar or text field using a couple of native SQL string functions. String functions are well worth becoming acquainted with as they can help make your code more effective and readable. These may be employed to trim off extra spaces or characters, determine how long a string is, and concatenate several field values together. If it is really necessary, this problem can be solved by building a computer column and an index on it, but this is out of the scope of this article.Counting String Occurrences in SQL Jby Robert GravelleĪlthough not as proficient at string manipulation as procedural programming languages such as Java, C++, and PHP, SQL does provide many functions for working with string data. The reason is that, if there is an index on the summary column, it cannot be used because the query optimizer cannot make assumptions on the results of the expressions. Nothing prevents us to use those expressions in a WHERE clause or in an ORDER BY clause, but this may heavily affect performance. In the examples above, the expressions should be relatively fast (though, of course, it can be a problem when applied to a huge number of rows). It’s not used with LEN() because the case obviously doesn’t affect a string length. In both cases, LOWER() is applied before REPLACE(), to make it work when. (LEN(summary) - LEN(REPLACE(LOWER(summary), LOWER('France'(,''))) / LEN('France') LEN(summary) - LEN(REPLACE(LOWER(summary), LOWER('x'), ''))Īny number of characters, case insensitive: SELECT Single character, case insensitive: SELECT We can make them case-insensitive by using the LOWER() function. The above expressions are case-sensitive. If there are zero occurrences the expression will still work, because zero divided by any number returns zero. So, for example, if the length difference is 6 there is one occurrence, and if the length difference is 12 there are two occurrences.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |