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Posted by jpluimers on 2022/10/27
I knew there was JSFiddle for live playing around with JavaScript and more in your browser, so I wondered if there was a similar site for databases and SQL queries.
There are, so here are a few database fiddle sites: SQL playgrounds where you can live play with SQL queries (sometimes even without an underlying example database).
All via [Wayback/Archive.is] database fiddle – Google Search:
Posted in Conference Topics, Conferences, Database Development, DB2, Development, Event, Firebird, JavaScript/ECMAScript, JSFiddle, MariaDB, MySQL, OracleDB, PL/SQL, PostgreSQL, Scripting, Software Development, SQL, SQL Server, SQLite, T-SQL | Leave a Comment »
Posted by jpluimers on 2022/01/06
Contrary to what many believe is that MySQL utf8 is not always full blown UTF-8 support, but actually utf8mb3, which has been deprecated for a while now.
Only utf8mb4 will give you full blown UTF-8 support.
This when someone reminded me of this in a Delphi application:
When I insert :joy: emoji into mysql varchar filed I got an error :
#22007 Incorrect string value: '\xF0\x9F\x98\x82' for column 'remarks' at row 1database charset is
utf8
Note that the :joy: emoji is 😂 and has Unicode code point U+1F602 which is outside the basic multilingual plane.
See:
- Kristian Köhntopp
»Where does PostgreSQL’s collation logic come from?
PostgreSQL relies on external libraries to order strings.
– libc, meaning the operating system locale facility (POSIX or Windows)
– icu, meaning the ICU project (if PostgreSQL was built with ICU support)«- MySQL does things differently:
MySQL binary data files are independent of the host operating system in byte order, number representation (as long as the host fulfils MySQLs basic requirements), collation and even time zone handling.- So MySQL implements collations internally, also to guarantee stability across OS updates.
If it didn’t, a libc update changing collations would mean you have to recreate a lot of indexes. Also, you would not be able to safely move data files from host to host.- MySQL also, for quite some time now, no longer updates its own charsets and collations internally, for the same reason.
So utf8 in MySQL is utf8mb3, the three byte variant of Unicode UTF-8 implementation that covers only the BMP (unicode up to U+FFFF).- When moving to fuller (multiplane) UTF-8 support, a new name was needed, and utf8mb4 was chosen.
So when you actually want modern utf8 in MySQL, you have to use utf8mb4, and now you know why.- utf8 is deprecated and will be upgraded to utf8mb4 in some future MySQL release. This will be a breaking upgrade, and I wonder if it will require dropping and recreating all indexes affected by the change.
That will be painful.- https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb3.html …
utf8mb3 page in the MySQL 8.0 manual, with deprecation notice.
What will change is the meaning of the alias utf8 (currently an alias for utf8mb3).
utf8mb3 Character Set (3-Byte UTF-8 Unicode Encoding)
utf8is an alias forutf8mb3; the character limit is implicit, rather than explicit in the name.NoteThe
utf8mb3character set is deprecated and you should expect it to be removed in a future MySQL release. Please useutf8mb4instead. Althoughutf8is currently an alias forutf8mb3, at some pointutf8is expected to become a reference toutf8mb4. To avoid ambiguity about the meaning ofutf8, consider specifyingutf8mb4explicitly for character set references instead ofutf8.
utf8mb4contrasts with theutf8mb3character set, which supports only BMP characters and uses a maximum of three bytes per character:
- For a BMP character,
utf8mb4andutf8mb3have identical storage characteristics: same code values, same encoding, same length.- For a supplementary character,
utf8mb4requires four bytes to store it, whereasutf8mb3cannot store the character at all. When convertingutf8mb3columns toutf8mb4, you need not worry about converting supplementary characters because there are none.
–jeroen
Posted in Conference Topics, Conferences, Database Development, Delphi, Development, Encoding, Event, MySQL, Software Development, UTF-8, UTF8 | Leave a Comment »
Posted by jpluimers on 2021/07/13
Configured properly, even across network (see the answers in the Twitter thread below).
[WayBack] Thread by @isotopp: “How fast is MySQL? I was casually operating under the impression, that a typical query resolution time is ~3ms. Turns out I was off one or e […]”
How fast is MySQL?
I was casually operating under the impression, that a typical query resolution time is ~3ms.
Turns out I was off one or even two orders of magnitude.
A “select version()” type of nonquery is handled in around 20µs.A typical query in a point-query or BKA environment (where id = const, … where id in (c1, c2, …)) is typically handled in 350µs.This is based on looking at
select event_name,
AVG_TIMER_WAIT/1000000 as avg_us, max_timer_wait/1000000 as max_us, min_timer_wait/1000000 as min_us from performance_schema.events_statements_summary_global_by_event_name
where event_name = ‘statement/sql/select’;| event_name | avg_us | max_us | min_us |
+———————-+———-+———–+———+
| statement/sql/select | 336.4440 | 2218.0450 | 36.4460 |for about any of our servers with that kind of workload that I have been looking at.This is obviously answered mostly from the buffer pool, because if you look at storage latencies, what you see here is that MySQL is in the same ballpark as NVME or SSD storage latencies (within 2x).TL;DR: MySQL is fucking fast, and I had no idea how to quantify fucking fast before I looked into P_S
Posted in Database Development, Development, MySQL, Software Development | Leave a Comment »
Posted by jpluimers on 2021/07/08
For my link archive: [WayBack] Case sensitivity for SQL identifiers · ontop/ontop Wiki · GitHub:
- Oracle and H2 changes unquoted identifiers to uppercase.
- Although technically possible, Oracle explicitly recommends to not use lowercase identifers. We do not support H2 with the setting DATABASE_TO_UPPER=FALSE, if this setting is enabled all queries with names and tables in lowercase must be quoted.
- DB2 Names are not case sensitive.
- For example, the table names CUSTOMER and Customer are the same, but object names are converted to uppercase when they are entered. If a name is enclosed in quotation marks, the name becomes case sensitive. The schema name is case-sensitive, and must be specified in uppercase characters.
- Postgres changes unquoted identifiers (both columns and alias names) to lowercase.
- Mysql does not change the case of unquoted tables and schemas.
- It changes in lowercase the unquoted columns. Mysql tables are stored as files in the operating system the server runs on. This means that database and table names are not case sensitive in Windows, and case sensitive in most varieties of Unix or Linux. The backtick ` is used for enclosing identifiers such as table and column names.
- Mssqlserver All connection string property names are case-insensitive.
- For example, Password is the same as password. Identifiers of objects in a database, such as tables, views, and column names, are assigned the default collation of the database. For example, two tables with names that differ only in case can be created in a database that has case-sensitive collation, but cannot be created in a database that has case-insensitive collation. Default SQL Server is not case sensitive. SELECT * FROM SomeTable is the same as SeLeCT * frOM soMetaBLe. Delimited identifiers are enclosed in double quotation marks (“) or brackets ([]). Identifiers that comply with the rules for the format of identifiers may or may not be delimited.
–jeroen
Posted in Database Development, DB2, Development, MySQL, OracleDB, PostgreSQL, SQL Server | Leave a Comment »
Posted by jpluimers on 2021/02/18
is a documentation browser that finds the relevant docs for your code. It works by parsing the code and connecting parts of it to their explanation in the docs
, and supports these languages:
You can enter any language text, then click the language, followed by clicking the “SHOW ME THE DOCS!” button, for which an example is further below.
The site has an open architecture, allowing to plug in more languages and documentation:
So for instance the below ./git/config file leads to this result [WayBack] where you can click on all the coloured areas for easy navigation through the documentation:
Posted in *nix, *nix-tools, Database Development, Development, DVCS - Distributed Version Control, git, MySQL, nginx, PostgreSQL, Power User, Software Development | Leave a Comment »
The Wiert Corner - irregular stream of stuff 