我正在使用Postgres，我正在尝试编写这样的查询：
select count(*) from table where datasets = ARRAY[]
即。我想知道有多少行对于某个列有一个空数组，但是postgres不喜欢这样：
select count(*) from super_eds where datasets = ARRAY[];
ERROR: syntax error at or near "]"
LINE 1: select count(*) from super_eds where datasets = ARRAY[];
^
答案 0 :(得分：77)
语法应为：
SELECT
COUNT(*)
FROM
table
WHERE
datasets = '{}'
使用引号和花括号来显示数组文字。
答案 1 :(得分：15)
您可以使用array_upper和array_lower函数在空数组上返回null的事实 ，所以你可以：
select count(*) from table where array_upper(datasets, 1) is null;
答案 2 :(得分：2)
Solution Query:
var coord;
function change_coord(location) {
var geocoder = new google.maps.Geocoder();
geocoder.geocode({'address': location}, function(results, status) {
if (status == google.maps.GeocoderStatus.OK) {
//real_lat and real_lng are int values
var real_lat = results[0].geometry.location.lat();
var real_lng = results[0].geometry.location.lng();
coord = {lat: real_lat, lng: real_lng};
}
});
console.log(coord); //undefined
}
Example:
table_emp：
body {
background-color: #558C89;
/*background-color: #1FDA9A;*/
color: #000305; /*remove if background is not working */
font-size: 87.5%; /*base font size is 14px */
font-family: Arial, 'Lucida Sans Unicode';
line-height: 1.5;
text-align: left;
margin-left: 21.5%;
}
a {
text-decoration: none;
}
a:link, a:visited {
}
a:hover, a:active {
}
.body {
}
form {
display: inline;
}
#logo {
position: absolute;
z-index: 1;
left: 0;
top: 5px;
height: 50px;
vertical-align: top;
}
.mainheader img {
width: 100%;
height: auto;
margin: 0% 0%;
}
.mainheader nav {
background-color: #424242;
/*background-color: #008BBA; /* Here for color of navigated buttons*/
height: 65px;
width: 100%;
position: absolute;
top: 0;
left: 0;
border-radius: 5px;
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
border-style: solid;
border-color: black;
border-width: 1px;
}
.mainheader nav ul {
list-style: none;
margin: 0 auto;
}
.mainheader nav ul li {
float: right;
display: inline;
margin-top: 0px;
}
.mainheader nav a:link, .mainheader nav a:visited {
color: #FFF;
font-weight: bold;
display: inline-block;
padding: 18px 25px;
height: 10px;
/* Come back here to continue to edit buttons */
}
.mainheader nav a:hover, .mainheader nav a:active, .mainheader nav .active a:link,
.mainheader nav .active a:visited {
background-color: #638CA6;
opacity: 0.85;
height: 63px;
text-shadow: none;
}
.mainheader nav ul li a {
border-radius: 5px;
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
}
.newsClass{
position: absolute;
width: 1000px;
background-color: #404040;
border-style: solid;
border-color: black;
border-width: 1px;
text-align: center;
color: #FFF;
margin: -100px 0 0 -150px;
top: 25%;
left: 27%;
z-index: 2;
}
.topcontent {
background-color: #404040;
width: 850px;
position: absolute;
text-align: center;
color: #FFF;
margin-top: 120px;
border-style: solid;
border-color: black;
border-width: 1px;
line-height: 1;
display: inline-block;
left: 21.5%;
}
#box{
border: 1px solid rgb(200, 200, 200);
box-shadow: rgba(0, 0, 0, 0.1) 0px 5px 5px 2px;
background: rgba(200, 200, 200, 0.1);
border-radius: 4px;
top:50px;
}
h2{
text-align:center;
color:#fff;
}
#footer {
color: #FFF;
}答案 3 :(得分：2)
如果您像我一样在2020年发现这个问题，正确的答案是
select count(*) from table where cardinality(datasets) = 0
cardinality已添加到PostgreSQL 9.4中，即〜2015
答案 4 :(得分：0)
SELECT COUNT(*)
FROM table
WHERE datasets = ARRAY(SELECT 1 WHERE FALSE)