allow Django like template SQL

[mashiike]

It seems that there is a need to templateize the SQL specified in task.
So, although it is simple, it can be templateized with Go Tamplate.
For the time being, we will not use a complicated template engine that can define macros.

example

CREATE DATABASE IF NOT EXISTS {{ must_env `ENV` }}_mysqlbatch;
USE {{ must_env `ENV` }}_mysqlbatch;
DROP TABLE IF EXISTS {{ var `relation` `hoge` }};
CREATE TABLE {{ var `relation` `hoge` }} (
    id INTEGER auto_increment,
    name VARCHAR(191),
    age INTEGER,
    PRIMARY KEY (`id`),
    UNIQUE INDEX `name` (`name`)
);
INSERT IGNORE INTO {{ var `relation` `hoge` }}(name) VALUES(CONCAT(SUBSTRING(MD5(RAND()), 1, 40),'@example.com'));
INSERT IGNORE INTO {{ var `relation` `hoge` }}(name) SELECT (CONCAT(SUBSTRING(MD5(RAND()), 1, 40),'@example.com')) FROM {{ var `relation` `hoge` }};
INSERT IGNORE INTO {{ var `relation` `hoge` }}(name, age) SELECT (CONCAT(SUBSTRING(MD5(RAND()), 1, 40),'@example.com')),RAND() FROM {{ var `relation` `hoge` }};
INSERT IGNORE INTO {{ var `relation` `hoge` }}(name, age) SELECT (CONCAT(SUBSTRING(MD5(RAND()), 1, 40),'@example.com')),RAND() FROM {{ var `relation` `hoge` }};
INSERT IGNORE INTO {{ var `relation` `hoge` }}(name, age) SELECT (CONCAT(SUBSTRING(MD5(RAND()), 1, 40),'@example.com')),RAND() FROM {{ var `relation` `hoge` }};
SELECT * FROM {{ var `relation` `hoge` }} WHERE age is NOT NULL LIMIT {{ must_var `limit` }};

$ go run cmd/mysqlbatch/main.go -h 127.0.0.1 --port 3306 -p mysqlbatch < testdata/test_template.sql --var limit=5 --var relation=hoge
2023/05/29 16:30:16 SELECT * FROM hoge WHERE age is NOT NULL LIMIT 5
+----+----------------------------------------------+-----+
| ID |                     NAME                     | AGE |
+----+----------------------------------------------+-----+
|  3 | 6b2d194aa6dfbe5886f089370c495af1@example.com |   1 |
|  4 | a998323e72b5582cf86c260f4d5c0f0a@example.com |   0 |
|  6 | 14c5b540fae3b60c26e703aaf58b4e13@example.com |   1 |
|  7 | cec2abd710bbce6cc899099d529b47b6@example.com |   1 |
|  8 | 17ac7a29e132612c2964ba2d78f7a3ca@example.com |   0 |
+----+----------------------------------------------+-----+


2023/05/29 16:30:16 DB time when the last SQL was executed: 2023-05-29 16:30:16 +0000 UTC