# 融合查询语法
etl-engine引擎中的融合查询提供将多源数据在内存中重组关联查询并输出查询结果的能力。
融合查询语法遵循ANSI SQL标准，与常规MySQL查询语法很相似。
- 支持对多种类别数据库之间读取的数据进行融合查询。
- 支持消息流数据传输过程中动态产生的数据与多种类型数据库之间的流计算查询。
- 融合查询语法遵循ANSI SQL标准。

## 样本

```shell
SELECT
    t_u.u_id,t_u.u_name,t_u.u_phone,
    t_o.o_id,t_o.o_price,t_o.o_number,t_o.o_money,t_o.o_writetime,
    t_p.p_id,t_p.p_name,t_p.p_contacts,t_p.p_desc  
FROM  t_u
    inner JOIN  t_o  
    ON t_o.u_id=t_u.u_id
    inner JOIN  t_p
    ON t_o.p_id=t_p.p_id
ORDER BY  
    INTEGER(SUBSTRING(t_u.u_id,3))  ASC
```

## 语法格式

- select 支持

```shell
SELECT
      [DISTINCT] field [, field ...]
      FROM table [, table ...]
      [WHERE condition]
      [GROUP BY field [, field ...] ]
      [HAVING condition]
   [ORDER BY order_item [, order_item ...] ]
   [LIMIT number_of_records [OFFSET number_of_records ] ]
```

- table 支持
INNER JOIN、LEFT JOIN、RIGHT JOIN、OUTER  JOIN、CROSS JOIN等


## 运算符支持

```shell
+ - * / == < <= > >= <> != || IS BETWEEN IN LIKE NOT ANY AND OR INTERSECT UNION EXCEPT EXISTS
```

## 函数支持

### 逻辑函数

```shell
COALESCE(value [, value ...])
IF(condition, value1, value2)
IFNULL(value1, value2)
NULLIF(value1, value2)
```

### 数字函数（30多个）

```shell
ABS(number)
ACOS(number)
ACOSH(number)
ASIN(number)
ASINH(number)
ATAN(number)
ATAN2(number2, number1)
ATANH(number)
CBRT(number)
CEIL(number)
COS(number)
COSH(number)
EXP(number)
EXP2(number)
EXPM1(number)
FLOOR(number)
IS_INF(number [, sign])
IS_NAN(number)
LOG(number)
LOG10(number)
LOG1P(number)
LOG2(number)
LOGB(number)
POW(base, exponent)
ROUND(number)
SIN(number)
SINH(number)
SQRT(number)
TAN(number)
TANH(number)
BIN_TO_DEC(bin)
OCT_TO_DEC(oct)
HEX_TO_DEC(hex)
ENOTATION_TO_DEC(enotation)
BIN(integer)
OCT(integer)
HEX(integer)
ENOTATION(float)
NUMBER_FORMAT(number [, precision, decimalPoint, thousandsSeparator, decimalSeparator])
RAND(min, max)
```

### 日期函数（30多个）

```shell
NOW()
DATETIME_FORMAT(datetime, format)
YEAR(datetime)
MONTH(datetime)
DAY(datetime)
HOUR(datetime)
MINUTE(datetime)
SECOND(datetime)
MILLISECOND(datetime)
MICROSECOND(datetime)
NANOSECOND(datetime)
WEEKDAY(datetime)
UNIX_TIME(datetime)
UNIX_NANO_TIME(datetime)
DAY_OF_YEAR(datetime)
WEEK_OF_YEAR(datetime)
ADD_YEAR(datetime, duration)
ADD_MONTH(datetime, duration)
ADD_DAY(datetime, duration)
ADD_HOUR(datetime, duration)
ADD_MINUTE(datetime, duration)
ADD_SECOND(datetime, duration)
ADD_MILLI(datetime, duration)
ADD_MICRO(datetime, duration)
ADD_NANO(datetime, duration)
TRUNC_MONTH(datetime)
TRUNC_DAY(datetime)
TRUNC_TIME(datetime)
TRUNC_MINUTE(datetime)
TRUNC_SECOND(datetime)
TRUNC_MILLI(datetime)
TRUNC_MICRO(datetime)
TRUNC_NANO(datetime)
DATE_DIFF(datetime1, datetime2)
TIME_DIFF(datetime1, datetime2)
TIME_NANO_DIFF(datetime1, datetime2)
UTC(datetime)
MILLI_TO_DATETIME(unix_milliseconds)
NANO_TO_DATETIME(unix_nano_time)
```

### 字符串函数（20多个）

```shell
TRIM(str)
LTRIM(str)
RTRIM(str)
UPPER(str)
LOWER(str)
BASE64_ENCODE(str)
BASE64_DECODE(str)
HEX_ENCODE(str)
HEX_DECODE(str)
LEN(str)
SUBSTRING(str, position [, len])
SUBSTR(str, position [, len])
INSTR(str, substr)
LIST_ELEM(str, sep, index)
REPLACE(str, old, new)
REGEXP_MATCH(str, regexp [, flags])
REGEXP_FIND(str, regexp [, flags])
TITLE_CASE(str)
```

### 加密函数

```shell
MD5(str)     
SHA1(str)     
SHA256(str)     
SHA512(str)     
MD5_HMAC(str,key_str)     
SHA1_HMAC(str,key_str)  
SHA256_HMAC(str,key_str)      
SHA512_HMAC(str,key_str)      
```

### 类型转换函数

```shell
STRING(value)
INTEGER(value)
FLOAT(value)
DATETIME(value [, timezone])
BOOLEAN(value)
```

### 聚合函数

```shell
COUNT([DISTINCT] *)
MIN(expr)
MAX(expr)
SUM([DISTINCT] expr)
AVG([DISTINCT] expr)
```


# 参考资料

```shell

  etl-engine使用手册(https://github.com/hw2499/etl-engine)
  etl-crontab使用手册(https://github.com/hw2499/etl-engine/wiki/etl-crontab%E8%B0%83%E5%BA%A6)
  嵌入脚本开发(https://github.com/hw2499/etl-engine/wiki/%E5%B5%8C%E5%85%A5%E8%84%9A%E6%9C%AC%E5%BC%80%E5%8F%91)
  etl-engine配置样例(https://github.com/hw2499/etl-engine/wiki/etl-engine%E4%BD%BF%E7%94%A8%E6%A0%B7%E4%BE%8B)


```