MySQL Bugs: #114333: Lead/lag window functions returning BLOB instead of VARCHAR

Bug #114333	Lead/lag window functions returning BLOB instead of VARCHAR
Submitted:	13 Mar 10:50	Modified:	13 Mar 11:26
Reporter:	Pedro Ferreira	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: DML	Severity:	S3 (Non-critical)
Version:	8.0	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	window function

Description:
Connect the client with the `--column-type-info` option for detailed information in the result. Run:

CREATE TABLE t0 (c0 VARCHAR(513));
SELECT lag(t0.c0) OVER () FROM t0; --outputs BLOB

The same happens with the `lead` window function. The default value for this case is NULL, which should be within the VARCHAR range.

Is this an issue?

The compilation parameters are the same as issue 108148:

-DWITH_DEBUG=1 -DWITH_ASAN=ON -DWITH_UBSAN=ON and boost library version 1.77

How to repeat:
Run the statements above.

Hi Mr. Ferreira,

Thank you for your bug report.

This proves to be a bug in the code and in the documentation.

However, this is a very small bug.

It is just a tiny bug in the calculation of the length of the string attribute in the tuple.

String function will return BLOB for the lengths larger then 2048 bytes.

However, LAG and LEAD return log values, even when there is a single row with 10 characters inserted:

SELECT lag(t0.c0) OVER () FROM t0;
Field   1:  `lag(t0.c0) OVER ()`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       BLOB
Collation:  utf8mb4_0900_ai_ci (255)
Length:     8208
Max_length: 0
Decimals:   0
Flags:      BLOB

Length simply can not be 8208 ...... 

It impacts version 8.0 and all higher versions. It is repeatable on all platforms.

Verified as reported and as repeated with added analysis.

Thank you.