[doc](function)add docs for math even, signbit, gcd ,lcm (#2558)

## Versions 

- [x] dev
- [ ] 3.0
- [ ] 2.1
- [ ] 2.0

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- [x] Chinese
- [x] English

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Author: wumeibanfa

docs/sql-manual/sql-functions/scalar-functions/numeric-functions/even.md

@@ -0,0 +1,84 @@
+---
+{
+    "title": "EVEN",
+    "language": "en"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+## Description
+
+Round to next even number by rounding away from zero.
+
+## Syntax
+
+```sql
+EVEN(<a>)
+```
+
+
+## Parameters
+
+| Parameter | Description |
+| -- | -- |
+| `<a>` | A numeric expression to round to the next even integer |
+
+## Return Value
+
+Returns the smallest even integer that is greater than or equal to x when x > 0, or less than or equal to x when x < 0.
+
+## Examples
+
+```sql
+select even(2.9);
+```
+
+```text
++----------+
+| even(2.9) |
++----------+
+|        4 |
++----------+
+```
+
+```sql
+select even(-2.9);
+```
+
+```text
++-----------+
+| even(-2.9) |
++-----------+
+|       -4  |
++-----------+
+```
+
+```sql
+select even(4);
+```
+
+```text
++--------+
+| even(4) |
++--------+
+|      4 |
++--------+
+```

docs/sql-manual/sql-functions/scalar-functions/numeric-functions/gcd.md

@@ -0,0 +1,85 @@
+---
+{
+    "title": "GCD",
+    "language": "en"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+## Description
+
+Calculates the greatest common divisor (GCD) of two integers.
+
+## Syntax
+
+```sql
+GCD(<a>, <b>)
+```
+
+
+## Parameters
+
+| Parameter | Description |
+| -- | -- |
+| `<a>` | The first integer |
+| `<b>` | The second integer |
+
+## Return Value
+
+Returns the greatest common divisor of `<a>` and `<b>`.
+
+## Examples
+
+```sql
+select gcd(54, 24);
+```
+
+```text
++------------+
+| gcd(54,24) |
++------------+
+|          6 |
++------------+
+```
+
+```sql
+select gcd(-17, 31);
+```
+
+```text
++-------------+
+| gcd(17,31)  |
++-------------+
+|           1 |
++-------------+
+```
+
+```sql
+select gcd(0, 10);
+```
+
+```text
++-----------+
+| gcd(0,10) |
++-----------+
+|        10 |
++-----------+
+```

docs/sql-manual/sql-functions/scalar-functions/numeric-functions/lcm.md

@@ -0,0 +1,93 @@
+---
+{
+    "title": "LCM",
+    "language": "en"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+## Description
+
+Calculates the least common multiple (LCM) of two integers.Note that the result may overflow.
+
+## Syntax
+
+```sql
+LCM(<a>, <b>)
+```
+
+
+## Parameters
+
+| Parameter | Description |
+| -- | -- |
+| `<a>` | The first integer |
+| `<b>` | The second integer |
+
+## Return Value
+
+Returns the least common multiple of `<a>` and `<b>`.
+
+## Examples
+
+```sql
+select lcm(12, 18);
+```
+
+```text
++------------+
+| lcm(12,18) |
++------------+
+|         36 |
++------------+
+```
+
+```sql
+select lcm(0, 10);
+```
+
+```text
++-----------+
+| lcm(0,10) |
++-----------+
+|         0 |
++-----------+
+```
+
+```sql
+select lcm(-4, 6);
+```
+
+```text
++------------+
+| lcm(-4,6)  |
++------------+
+|          12|
++------------+
+```
+
+```sql
+select lcm(-170141183460469231731687303715884105728, 3);
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = Can not convert to legacy literal: 510423550381407695195061911147652317184
+```

docs/sql-manual/sql-functions/scalar-functions/numeric-functions/signbit.md

@@ -0,0 +1,83 @@
+---
+{
+    "title": "SIGNBIT",
+    "language": "en"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+## Description
+
+Determine whether the sign bit of the given floating-point number is set.
+
+## Syntax
+
+```sql
+SIGNBIT(<a>)
+```
+
+## Parameters
+
+| Parameter | Description |
+| -- | -- |
+| `<a>` | Floating-point number to check the sign bit for |
+
+## Return Value
+
+Returns true if the sign bit of `<a>` is set (i.e., `<a>` is negative), otherwise returns false.
+
+## Examples
+
+```sql
+select signbit(-1.0);
+```
+
+```text
++-----------------------------+
+| signbit(cast(-1 as DOUBLE)) |
++-----------------------------+
+| true                        |
++-----------------------------+
+```
+
+```sql
+select signbit(0.0);
+```
+
+```text
++----------------------------+
+| signbit(cast(0 as DOUBLE)) |
++----------------------------+
+| false                      |
++----------------------------+
+```
+
+```sql
+select signbit(1.0);
+```
+
+```text
++----------------------------+
+| signbit(cast(1 as DOUBLE)) |
++----------------------------+
+| false                      |
++----------------------------+
+```