I "googled" and found a magical and elegant sql query to split a comma-separated input string into rows in a single column. Doing so allows a join instead of a "where in". It used a select into or insert into combined with a select, coalesce() and where to create rows, one for each value in the string.
There are plenty of examples using coalesce() to form a string but none (any more) to split it. I've also found this solution for the meantime:
http://www.sqlservercentral.com/articles/T-SQL/62867/
But I'm curious now, that I cannot "regoogle" for the gem I found before (about a year ago).
Has anyone seen how to split a string with coalesce()? If so, how does its performance compare to the various sql string splitters that have been studied and compiled?
COALESCE simply returns the first non-null value from a group of expressions. It would not perform any magical splitting of a delimited string.
Related
Need to split column value into multiple columns based on delimiter,
Also need to create columns dynamically based on no. of delimiters, delimiter could be comma or so. Thanks,
You might be better off working with an array in this case. You haven't specified whether each record will have the same number of delimiters, so dynamically creating columns for tables will take some scripting. If they are, you could potentially use a SPLIT, LATERAL FLATTEN, and PIVOT, but the pivot needs static column names, so you'll likely need a stored procedure to deal with that.
To answer your first question, you can use SPLIT and/or SPLIT_PART to split the column into values. The SPLIT function creates an array for you, while the SPLIT_PART function creates the array, but outputs a single value from the array.
https://docs.snowflake.com/en/sql-reference/functions/split.html
https://docs.snowflake.com/en/sql-reference/functions/split_part.html
https://docs.snowflake.com/en/sql-reference/functions/flatten.html
https://docs.snowflake.com/en/sql-reference/constructs/pivot.html
I am running below query in Teradata :
sel requesttext from dbc.tables
where tablename='old_employee_table'
Result:
alter table DB_NAME.employee_table,no fallback ;
I want to get below result using SQL:
DB_NAME.employee_table
Requesttext can be:
create set table DB_NAME.employee_table;
DB Name and table can occur anywhere in the result. Since .(dot) is joining them that's why i want to split with .(dot).
Basically I need sql which can result me surrounding values of .(dot)
I want DBName and Tablename in result.
I'm not a Teradata person, but this should work for both strings given so far, as long as teradata's regexp_substr() supports positive look-behind and positive look-ahead assertions (I might have the Teradata syntax wrong, so a little tweaking may be needed):
SELECT REGEXP_SUBSTR(requesttext, '(?<= )(\w+\.\w+)(?=[,$]?)', 1, 1)
FROM dbc.tables
WHERE tablename='old_employee_table'
See the regex101 example. Hopefully it translates to Teradata easily.
The regex looks for and returns the words either side of and including the period, when preceded by a space, and followed by an optional comma or the end of the line.
You could do this with either regexp_substr() or strtok().
As Jamie Zawinski said:
Some people, when confronted with a problem, think "I know, I'll use
regular expressions." Now they have two problems.
So I would go with the strtok() method. Also I'm lazy and regular expressions are hard.
Function strtok() takes three arguments:
The string being split
The delimiter to split the string
The number of the token to grab.
To get at the <database>.<table> from that string that is returned in your query, we can split by a space, grab the third token, then split that by a comma and grab the first token.
That would look like:
SELECT strtok(strtok(requestText,' ',3),',',1)
FROM dbc.tables
WHERE tablename='old_employee_table'
I have a query that is returning data from a database. In a single field there is a rather long text comment with a segment, which is clearly defined with marking tags like !markerstart! and !markerend!. I would like to have a query return with the string segment between the two markers removed (and the markers removed too).
I would normally do this client-side after I get the data back, however, the problem is that the query is an INSERT query that gets it's data from a SELECT statement. I don't want the text segment to be stored in the archival/reporting table (working with an OLTP application here), so I need to find a way to get the SELECT statement to return exactly what is to be inserted, which, in this case, means getting the SELECT statement to strip out the unwanted phrase instead of doing it in post-processing client-side.
My only thought is to use some convoluted combination of SUBSTRING, CHARINDEX, and CONCAT, but I'm hoping there is a better way, but, based on this, I don't see how. Anyone have ideas?
Sample:
This is a long string of text in some field in a database that has a segment that needs to be removed. !markerstart! This is the segment that is to be removed. It's length is unknown and variable. !markerend! The part of this field that appears after the marker should remain.
Result:
This is a long string of text in some field in a database that has a segment that needs to be removed. The part of this field that appears after the marker should remain.
SOLUTION USING STUFF:
I really don't like how verbose this is, but I can put it in a function if I really need to. It isn't ideal, but it is easier and faster than a CLR routine.
SELECT STUFF(CAST(Description AS varchar(MAX)), CHARINDEX('!markerstart!', Description), CHARINDEX('!markerend!', Description) + 11 - CHARINDEX('!markerstart!', Description), '') AS Description
FROM MyTable
You may want to consider implementing a CLR user-defined function that returns the parsed data.
The following link demonstrates how to use a CLR UDF RegEx function for pattern matching and data extraction.
http://msdn.microsoft.com/en-us/magazine/cc163473.aspx
Regards,
You can use Stuff function or Replace function and replace your unwanted symbols with ''.
STUFF('EXP',START_POS,'NUMBER_OF_CHARS','REPLACE_EXP')
I'm selecting columns from one table and would like to select all values of a column from a related table when the two tables have a matching value, separate them by commas, and display them in a single column with my results from table one.
I'm fairly new to this and apologize ahead of time if I'm not wording it correctly.
It sounds like what you're trying to do is to take multiple rows and aggregate them into a single row by concatenating string values from one or more columns. Yes?
If that's the case, I can tell you that it's a more difficult problem than it seems if you want to do it using portable SQL - especially if you don't know ahead of time how many items you may get.
The Oracle-specific solution often used in such cases is to implement a custom aggregate function - STRAGG(). Here's a link to an article that describes exactly how to do so and has examples of it's usage.
If you're on Oracle 9i or later and are willing to live with using undocumented functions (that could change in the future), you can also look at the WM_CONCAT() function - which does much the same thing.
You want a row aggregation or concatenation function, choices are:
If you are using Oracle 11gR2, there is a built-in function to aggregate strings with a delimiter called LISTAGG(column, delimiter).
If you are using any earlier release of Oracle database, you can use WM_CONCAT(column) function, however you have no choice of delimiter and will have to use something like TRANSLATE(string, string_to_replace, replacement_string) function to change the delimiter afterwards if your data does not contain commas.
As mentioned by LBushkin, you can create a custom function in your schema to perform row aggregation for you. Here is PL/SQL code example for one: http://www.oracle-base.com/articles/misc/StringAggregationTechniques.php#user_defined_aggregate_function
I'm working on an app that involves a lot of carefully designed strings. I'm in the process of designing the string format and for that I need to know what's possible and what's not when I'm querying the same data.
Which ones of these are possible with MySQL? .. and how do I accomplish them?
Results which contain this exact string -- not case sensitive
Results which contain this exact string -- case sensitive
Results which contain a similar string -- not case sensitive
Results which contain a similar string -- but individual characters must be of the same case
1. Results which contain this exact string -- not case sensitive
2. Results which contain this exact string -- case sensitive
These can both be accomplished. See the page documenting string functions in MySQL, in particular INSTR.
Case sensitivity is determined by the collation of a column. If you want values in a column to be compared in a case-sensitive fashion, then you give it a case-sensitive collation, as in the following example:
ALTER TABLE MyTable ADD MyColumn VARCHAR(10) CHARACTER SET ascii COLLATE ascii_general_cs NOT NULL
Conversely, if you want values in a column to be compared in a case-insensitive fashion, then give it a case-insensitive collation.
If you might want values in a column to be compared either way, then there are ways to do that too, though it's slightly more complicated.
3. Results which contain a similar string -- not case sensitive
4. Results which contain a similar string -- but individual characters must be of the same case
Depends what exactly you mean by "similar", but for some values of "similar" yes this is available. You will probably find it useful to consult the page I linked above.
SELECT this FROM that WHERE LOWER(string) = LOWER("blablabla");
SELECT this FROM that WHERE string = "blablabla";
SELECT this FROM that WHERE LOWER(string) LIKE LOWER("blablabla");
SELECT this FROM that WHERE string LIKE "blablabla";
Hope that's right.