Details
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Technical task
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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None
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None
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10.2.2-3, 10.2.2-1, 10.2.2-2, 10.2.2-4, 10.1.18
Description
As of version 10.3.1, Item_func_case (when handling a simple CASE) stores the predicant argument (in the args[] array) after the WHEN..THEN arguments and before the ELSE argument.
For example, this expression:
CASE pred WHEN search1 THEN res1 WHEN search2 THEN res2 ELSE resE END |
stores the arguments as follows:
- args[0]=search1
- args[1]=res1
- args[2]=search2
- args[3]=res2
- args[4]=pred
- args[6]=resE
Under terms of this task we'll do the following:
1. Change Item_func_case to store the arguments in the order of their appearance in the parser: the predicant argument in args[0], followed by the WHEN..THEN..ELSE arguments
2. Split Item_func_case into two separate classes Item_func_case_simple and Item_func_case_searched (for CASE expressions with and without predicant respectively).
3. Change the constructors of the affected classes just to accept a List<Item> argument (without additional first_expr_arg and else_expr_arg.
Advantages:
a. #1 and #3 will help to simplify the code in sql_yacc_ora.yy
| DECODE_SYM '(' expr ',' decode_when_list ')' |
{
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// 30 lines of the code, extracting {{else_expr_arg}} from the list. |
}
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to something as simple as:
| DECODE_SYM '(' expr ',' decode_when_list ')' |
{
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$5->push_front($3, thd->mem_root);
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if (!($$= new (thd->mem_root) Item_func_case_simple(thd, *$5))) |
MYSQL_YYABORT;
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}
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b. #1 and #3 will help to implement MDEV-13863 easier. MDEV-13836 will introduce a new class Item_func_decode_oracle. Without #1, we'd have to use the same complex code from sql_yacc_ora.yy, now for both DECODE() and DECODE_ORACLE().
c. #2 will slightly reduce the memory size required to handle searched CASE expression, because only Item_func_case_simple will need to derive from Predicant_to_list_comparator
d. #2 will make the code more readable by removing a lot of if statements like this:
if (first_expr_num != -1) |
{
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...
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}
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else
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{
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...
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}
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as the branches for the searched and the simple CASE expressions will reside in methods of different classes.
e. #1 will make it easier to debug the code in gdb, as printing the arguments in their syntactic order will be much easier than now.
Attachments
Issue Links
- blocks
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MDEV-13863 sql_mode=ORACLE: DECODE does not treat two NULLs as equivalent
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- Closed
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Activity
| Field | Original Value | New Value |
|---|---|---|
| Link |
This issue blocks |
| Description |
As of version {{10.3.1}}, {{Item_func_case}} (when handling a simple {{CASE}}) stores the predicant argument (in the {{args[]}} array) after the {{WHEN..THEN}} arguments and before the {{ELSE}} argument.
For example, this expression: {code:sql} CASE pred WHEN search1 THEN res1 WHEN search2 THEN res2 ELSE resE END {code} stores the arguments as follows: - args[0]=search1 - args[1]=res1 - args[2]=search2 - args[3]=res2 - args[4]=pred - args[6]=resE Under terms of this task we'll do the following: 1. Change {{Item_func_case}} to store the arguments in the order of their appearance in the parser: the predicant argument in args[0], followed by the {{WHEN..THEN..ELSE}} arguments 2. Split {{Item_func_case}} into two separate classes {{Item_func_case_simple}} and {{Item_func_case_searched}} (for {{CASE}} expressions with and without predicant respectively). 3. Change the constructors of the affected classes just to accept a {{List<Item>}} argument (without additional {{first_expr_arg}} and {{else_expr_arg}}. Advantages: a. #1 and #3 will help to simplify the code in {{sql_yacc_ora.yy}} {code:cpp} | DECODE_SYM '(' expr ',' decode_when_list ')' { // 30 lines of the code, extracting {{else_expr_arg}} from the list. } {code} to something as simple as: {code:cpp} | DECODE_SYM '(' expr ',' decode_when_list ')' { $5->push_front($3, thd->mem_root); if (!($$= new (thd->mem_root) Item_func_case_simple(thd, *$5))) MYSQL_YYABORT; } {code} b. #1 and #3 will help to implement c. #2 will slightly reduce the memory size required to handle searched {{CASE}} expression, because only {{Item_func_case_simple}} will need to derive from {{Predicant_to_list_comparator}} d. #2 will make the code more readable by removing a lot of {{if}} statements like this: {code:cpp} if (first_expr_num != -1) { ... } else { ... } {code} as the branches for the searched and the simple {{CASE}} expressions will reside in methods of different classes. e. #1 will make it easier to debug the code in {{gdb}}, as printing the arguments in their syntactic order will be much easier than now. |
As of version {{10.3.1}}, {{Item_func_case}} (when handling a simple {{CASE}}) stores the predicant argument (in the {{args[]}} array) after the {{WHEN..THEN}} arguments and before the {{ELSE}} argument.
For example, this expression: {code:sql} CASE pred WHEN search1 THEN res1 WHEN search2 THEN res2 ELSE resE END {code} stores the arguments as follows: - args[0]=search1 - args[1]=res1 - args[2]=search2 - args[3]=res2 - args[4]=pred - args[6]=resE Under terms of this task we'll do the following: 1. Change {{Item_func_case}} to store the arguments in the order of their appearance in the parser: the predicant argument in {{args[0]}}, followed by the {{WHEN..THEN..ELSE}} arguments 2. Split {{Item_func_case}} into two separate classes {{Item_func_case_simple}} and {{Item_func_case_searched}} (for {{CASE}} expressions with and without predicant respectively). 3. Change the constructors of the affected classes just to accept a {{List<Item>}} argument (without additional {{first_expr_arg}} and {{else_expr_arg}}. Advantages: a. #1 and #3 will help to simplify the code in {{sql_yacc_ora.yy}} {code:cpp} | DECODE_SYM '(' expr ',' decode_when_list ')' { // 30 lines of the code, extracting {{else_expr_arg}} from the list. } {code} to something as simple as: {code:cpp} | DECODE_SYM '(' expr ',' decode_when_list ')' { $5->push_front($3, thd->mem_root); if (!($$= new (thd->mem_root) Item_func_case_simple(thd, *$5))) MYSQL_YYABORT; } {code} b. #1 and #3 will help to implement c. #2 will slightly reduce the memory size required to handle searched {{CASE}} expression, because only {{Item_func_case_simple}} will need to derive from {{Predicant_to_list_comparator}} d. #2 will make the code more readable by removing a lot of {{if}} statements like this: {code:cpp} if (first_expr_num != -1) { ... } else { ... } {code} as the branches for the searched and the simple {{CASE}} expressions will reside in methods of different classes. e. #1 will make it easier to debug the code in {{gdb}}, as printing the arguments in their syntactic order will be much easier than now. |
| Status | Open [ 1 ] | In Progress [ 3 ] |
| issue.field.resolutiondate | 2017-09-23 05:55:24.0 | 2017-09-23 05:55:24.309 |
| Fix Version/s | 10.3.2 [ 22533 ] | |
| Fix Version/s | 10.3 [ 22126 ] | |
| Resolution | Fixed [ 1 ] | |
| Status | In Progress [ 3 ] | Closed [ 6 ] |
| Parent | MDEV-10764 [ 57940 ] | |
| Issue Type | Task [ 3 ] | Technical task [ 7 ] |
| Parent | MDEV-10764 [ 57940 ] |
|
| Workflow | MariaDB v3 [ 82712 ] | MariaDB v4 [ 152857 ] |
| Zendesk Related Tickets | 165723 |
Pushed to bb-10.2-ext and 10.3