如何在 SQLite 中模拟 REPEAT()

Question

Most relational databases have some sort of REPEAT() string function, for instance:

SELECT REPEAT('abc', 3)

Would yield

abcabcabc

SQLite on the other hand has a very limited feature set. The functions supported by SQLite are listed here:

http://www.sqlite.org/lang_corefunc.html

Can REPEAT() be emulated with the functions available in SQLite?

Answer 1

A solution was inspired by this answer to a related question, here:

How to emulate LPAD/RPAD with SQLite

I wanted to share this on Stack Overflow, as this may be useful to other SQLite users. The solution goes like this:

-- X = string
-- Y = number of repetitions

replace(substr(quote(zeroblob((Y + 1) / 2)), 3, Y), '0', X)

Answer 2

If its a single character you want to repeat, you can use printf function.

Bellow is an example where x is repeated 10 times. The key is the * in the format string which specifies that the width of the field will be passed as a parameter:

sqlite> select printf('%.*c', 10, 'x');
xxxxxxxxxx

To repeat multiple characters you can then replace() each x by the longer string, much as in Lukas's answer above.

Answer 3

A simplified version of @Lukas Eder's solution using hex() instead of quote:

-- X = string
-- Y = number of repetitions

replace(hex(zeroblob(Y)), '00', X) 

Answer 4

My answer combines Shiplu Mokaddim's "printf character substitution repetition" with the "replace" of Steve Broberg and Lukas Eder :

sqlite> SELECT replace(printf('%.' || 5 || 'c', '/'),'/','My string ');
My string My string My string My string My string      

It's also easy to derive the number of repetitions from table data. Here's an example using a common table expression:

sqlite> WITH cte(string, reps) AS
    ..>   (SELECT * FROM (values ('alpha ', 1),('bravo ', 5),('charlie ', 3) ) )
    ..> SELECT *, replace(printf('%.' || reps || 'c', '/'), '/', string) FROM cte;
alpha       1           alpha
bravo       5           bravo bravo bravo bravo bravo
charlie     3           charlie charlie charlie