dbDelta Lowercase KEY Keyword Duplicates Indexes

[charlestonsw]

Reference ticket #10404.

This is to decompose the original ticket into components. May be fixed in 4.4. Needs testing.

---

Creates duplicate indexes:

create table x (
id mediumint(8) not null autoincrement,
key id (id)
)

Does not create duplicate indexes:

create table x (
id mediumint(8) not null autoincrement,
KEY id (id)
)

[ocean90]

In 37583:

Database: Normalize index definitions in dbDelta().

dbDelta() compares the index definitions against the result of SHOW INDEX FROM $table_name. This requires a specific format so indices are not unnecessarily re-created. This format wasn't ensured, until now.

• Parse the raw index definition to extract the type, name and columns so a normalized definition can be built (#20263, #34873).
• Standardize on uppercase types (#34871) and on 'KEY'. 'INDEX' is only a synonym for 'KEY'.
• Escape index names with backticks (#20263).
• Normalize columns: Ignore ASC and DESC definitions (#34959), remove whitespaces (#34869) and escape column names with backticks (#20263).
• Add backticks to all index change queries (#20263).

Props ocean90, pento, kurtpayne.
Fixes #20263, #34869, #34871, #34873, #34959.