add an example to illustrate json handling in mysql

see apache/datafusion-sqlparser-rs#1019

see #146

examples/mysql json handling/README.md

@@ -0,0 +1,6 @@
+# Handling json data in MySQL
+
+This demonstrates both how to produce json data from a SQL query in MySQL
+and how to consume json data from SQLPage.
+
+![](./screenshots/app.png)

examples/mysql json handling/docker-compose.yml

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+services:
+  web:
+    image: lovasoa/sqlpage:main # main is cutting edge, use lovasoa/sqlpage:latest for the latest stable version
+    ports:
+      - "8080:8080"
+    volumes:
+      - .:/var/www
+      - ./sqlpage:/etc/sqlpage
+    depends_on:
+      - db
+    environment:
+      DATABASE_URL: mysql://root:secret@db/sqlpage
+  db: # The DB environment variable can be set to "mariadb" or "postgres" to test the code with different databases
+    ports:
+      - "3306:3306"
+    image: mariadb:10.6 # support for json_table was added in mariadb 10.6
+    environment:
+      MYSQL_ROOT_PASSWORD: secret
+      MYSQL_DATABASE: sqlpage

examples/mysql json handling/index.sql

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+select 'form' as component, 'Create a new Group' as title, 'Create' as validate;
+select 'Name' as name;
+
+insert into groups(name) select :Name where :Name is not null;
+
+select 'list' as component, 'Groups' as title, 'No group yet' as empty_title;
+select name as title from groups;
+
+select 'form' as component, 'Add an user' as title, 'Add' as validate;
+select 'UserName' as name, 'Name' as label;
+select 
+    'Memberships[]'  as name,
+    'Group memberships' as label,
+    'select' as type,
+    TRUE     as multiple,
+    'press ctrl to select multiple values' as description,
+    json_arrayagg(json_object("label", name, "value", id)) as options
+from groups;
+
+insert into users(name) select :UserName where :UserName is not null;
+insert into group_members(group_id, user_id)
+select CAST(json_unquote(json_elems.json_value) AS INT), last_insert_id()
+from (
+    with recursive json_elems(n, json_value) as (
+        select 0, json_extract(:Memberships, '$[0]')
+        union all
+        select n + 1, json_extract(:Memberships, concat('$[', n + 1, ']'))
+        from json_elems
+        where json_value is not null
+    ) select * from json_elems where json_value is not null
+) as json_elems
+where :Memberships is not null;
+
+select 'list' as component, 'Users' as title, 'No user yet' as empty_title;
+select
+    users.name as title,
+    group_concat(groups.name) as description
+from users
+left join group_members on users.id = group_members.user_id
+left join groups on groups.id = group_members.group_id
+group by users.id, users.name;

examples/mysql json handling/sqlpage/migrations/0001_users_and_groups.sql

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+create table users (
+    id int primary key auto_increment,
+    name varchar(255) not null
+);
+
+create table groups (
+    id int primary key auto_increment,
+    name varchar(255) not null
+);
+
+create table group_members (
+    group_id int not null,
+    user_id int not null,
+    primary key (group_id, user_id),
+    foreign key (group_id) references groups (id),
+    foreign key (user_id) references users (id)
+);

examples/official-site/sqlpage/migrations/01_documentation.sql

@@ -324,8 +324,8 @@ This creates a more compact (but arguably less user-friendly) alternative to a s
 In this case, you should add square brackets to the name of the field.
 The target page will then receive the value as a JSON array of strings, which you can iterate over using 
  - the `json_each` function [in SQLite](https://www.sqlite.org/json1.html) and [Postgres](https://www.postgresql.org/docs/9.3/functions-json.html),
- - the [`JSON_TABLE`](https://dev.mysql.com/doc/refman/8.0/en/json-table-functions.html) function in MySQL (which you''ll need to wrap in a function, because SQLPage cannot parse the non-standard syntax of this function)
  - the [`OPENJSON`](https://learn.microsoft.com/fr-fr/sql/t-sql/functions/openjson-transact-sql?view=sql-server-ver16) function in Microsoft SQL Server.
+ - in MySQL, json manipulation is less straightforward: see [the SQLPage MySQL json example](https://github.com/lovasoa/SQLpage/tree/main/examples/mysql%20json%20handling)
 
 The target page could then look like this: