sql/expression: implement substring function #55
Conversation
41bb530 to
454063e
Compare
|
Done @ajnavarro |
454063e to
49f8464
Compare
sql/expression/function.go
Outdated
| return nil, fmt.Errorf("substring: invalid length %d", length) | ||
| } | ||
|
|
||
| if startIdx < 0 { |
There was a problem hiding this comment.
Take into account that:
- The first position in string is 1.
- If start_position is a positive number, then the SUBSTRING function starts from the beginning of the string.
- If start_position is a negative number, then the SUBSTRING function starts from the end of the string and counts backwards. Negative values for start_position was introduced in MySQL 4.1.
- If start_position is bigger than the string length, the result is NULL
- If start_position is 0, the result is NULL
There was a problem hiding this comment.
According to the link you provided:
If start position is 0, the result is ""
if start_position is bigger than string length result is ""
There was a problem hiding this comment.
I think the UI is wrong. Check with: SELECT SUBSTRING("SQL Tutorial", 5, 3) AS ExtractString, NULL as test; the output of test appears to be "" but it is NULL
There was a problem hiding this comment.
If you do SELECT NULL is null returns 1, and if you do SELECT SUBSTRING("fooo bar", 0) is null it returns 0, so in this case is not null what it returns. From what I see in that UI, the only way SUBSTRING returns null is if the string itself is null.
There was a problem hiding this comment.
https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_substring
If len is less than 1, the result is the empty string.
sql/expression/function.go
Outdated
| startIdx := start.(int64) | ||
| runeCount := int64(len(text)) | ||
|
|
||
| if length < 0 { |
There was a problem hiding this comment.
In mysql substring implementation length is optional
There was a problem hiding this comment.
Also, If length is bigger than the remained characters, no error happens
|
@erizocosmico You can check all corner cases here: https://www.w3schools.com/sql/trymysql.asp?filename=trysql_func_mysql_substring Do you mind to add tests for them? |
|
Yes, sure |
Fixes src-d#42 This PR implements the substring(str, start[, length]) function with the same behaviour as its homonym MySQL function. Since Go strings are UTF8, this function does not return a direct substring str[start:start+length], instead returns the substring of runes. That is, "á"[0:1] does not return a partial unicode glyph, but "á" itself. Signed-off-by: Miguel Molina <miguel@erizocosmi.co>
49f8464 to
1fe11f5
Compare
|
Fixed @ajnavarro |
Fixes #42
This PR implements the substring(str, start[, length]) function with the same rules as its homonym function in MySQL.
Since Go strings are UTF8, this function does not return a direct substring
str[start:start+length], instead returns the substring of runes. That is,"á"[0:1]does not return a partial unicode glyph, but"á"itself.