Question

所以我想计算并回显来自table2的行数，这些行与id具有相同的row table1。

我理解函数mysqli_num_rows功能，但是如何让rows来自table2的匹配id？

总新手，还在搜索。认为这可能有助于我朝着正确的方向前进。谢谢你的帮助！

Answer 1

mysqli_num_rows返回结果中的行数。您应该编写另一个查询来返回表2中具有相同ID

的行数

SELECT COUNT(*)
FROM table2
WHERE table2.id = <id>

Answer 2

CREATE TABLE table1 (id INT);
CREATE TABLE table2 (id INT);

INSERT INTO table1 VALUES (1), (2), (3), (4);
INSERT INTO table2 VALUES (2), (4);

SELECT COUNT(*)
  FROM table1
  JOIN table2
    ON table1.id = table2.id;

在此处试试：http://sqlfiddle.com/#!9/0d289/1

Answer 3

试试这个：

    SELECT `table2`.`id`, COUNT(`table2`.`id`) AS `num_rows`
    FROM `table2`
    LEFT JOIN `table1` ON `table2`.`id` = `table1`.`id`
    WHERE `table2`.`id` IS NOT NULL
    GROUP BY `table2`.`id`
    ORDER BY `table2`.`id` ASC

Answer 4

仅计算

select table2.id, count(*)
  from table1, table2
    where  table1.id = table2.id
  group by table2.id

知道什么是id和多少

//shader1
<script id="vshader1" type="x-shader/x-vertex">

#extension GL_EXT_draw_buffers : require
varying vec2 vUv;

void main(void){
    vUv = uv;
    gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
}
</script>

<script id="fshader1" type="x-shader/x-fragment">
uniform sampler2D texture;
varying vec2 vUv;
void main(void) {
    vec4 smpColor = texture2D(texture, vUv);
    gl_FragData[0] = smpColor;
    gl_FragData[1] = smpColor;
}
</script>

//shader2
<script id="vshader2" type="x-shader/x-vertex">
varying vec2 vUv;

void main(void){
    vUv = uv;
    gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
}
</script>

<script id="fshader2" type="x-shader/x-fragment">
uniform sampler2D texture;
varying vec2 vUv;
void main(void) {
    vec4 smpColor = texture2D(texture, vUv);
    gl_FragColor = smpColor;
}
</script>

The second case on sqlfiddle.com

计算具有相同id [PHP]

4 个答案: