PHP to PostgreSQL insert unnested arrays into multiple rows - php

Question

I have some data in PHP arrays/variables ready to insert into a PostgreSQL table via an INSERT statement.
For a simple example say I have the following information:
$name= 'someName';
$time = array(1,2,3);
$elevation = array(100,200,300);
(In my real application these are double precision and potentially 1,000+ values)
I also have my postgresql table with columns "name","time","elevation"
I want to insert these in a single INSERT statement, and have been given multiple different ways to do this.
Loop and insert one data point (row) at a time.
Use unnest() on the arrays and do a single insert (fastest)
My question is can I pass a single variable name, and the un-nested arrays and have name repeated every row (ever array element), or do I need to construct a repeated array for name the equivalent count() as the other arrays?
An example statement:
*cr_query is a custom PHP pg_query wrapper we use
cr_query($conn,"INSERT INTO sometable (name,time,elevation) VALUES ({$name},{unnest($time)},{unnest($elevation)}););
This would insert into sometable:
ID name time elevation
1 someName 1 100
2 someName 2 200
3 someName 3 300
Am I correct here or do I need to do something else?
EDIT:
Lets say I also have another variable "surface". Surface can be a double value or can be NULL. So I want to insert into the table to look like so:
ID name time elevation surface
1 someName 1 100 50
2 someName 2 200 NULL
3 someName 3 300 100
In PHP, using the method perscribed by klin below an array for surface in the unnest statement would become unnest(array[50,,100]); This throws an error like so:
(Error from my real data)
ERROR: syntax error at or near "," LINE 3: ...-6,5.75E-6,5.75E-6,5.75E-6,5.75E-6]),unnest(array[,,,,,,,,,]... ^
EDIT 2:
Now that all of the "encoding" is working a new problem has popped up. Say the example column "surface" above is type double precision.
Say I am inserting an array, but for this set all of the data is null.
The essential piece is:
unnest(array[null,null,null,null,null,null,null,null,null,null])
However, this array is of type string. Add a single value to it and it becomes the type of that numeric value, but I need to be able to handle this.
My question is: How do I insert an unnested array of all null values into a double precision column? (I tried to cast ::double precision) but it's not possible.

Answer 1

Assuming your cr_query() function is not doing any magic things, your code is going to raise postgres syntax error. You can use unnest but you must prepare proper query text.
Try your code:
$name= 'someName';
$time = array(1,2,3);
$elevation = array(100,200,300);
echo "INSERT INTO sometable (name,time,elevation) VALUES ".
"({$name},{unnest($time)},{unnest($elevation)})"
echo: INSERT INTO sometable (name,time,elevation) VALUES (someName,{unnest(Array)},{unnest(Array)})
Obviously it is not what we want to send to postgres. How to repair this?
$name= 'someName';
$time = array(1,2,3);
$elevation = array(100,200,300);
$timestr = 'array['. implode(',', $time). ']';
$elevstr = 'array['. implode(',', $elevation). ']';
echo "INSERT INTO sometable (name,time,elevation) ".
"VALUES ('$name',unnest($timestr),unnest($elevstr));"
echo: INSERT INTO sometable (name,time,elevation) VALUES ('someName',unnest(array[1,2,3]),unnest(array[100,200,300]));
I think this is correct query. Note that I enclosed text variable '$name' in single quotes.
If you have nulls in your arrays you have to replace all empty strings to 'null' in prepared text for query.
Probably the simplest way to do it is to use str_replace().
As the conversion is getting more complicated it is handy to write a function (say "pgstr()") for that purpose.
function pgstr($array) {
$str =
str_replace('[,', '[null,',
str_replace(',]', ',null]',
'array['. implode(',', $array). ']'));
while (strpos($str, ',,') > 0) $str = str_replace(',,', ',null,', $str);
return $str;
}
$name= 'someName';
$time = array(1,2,3,4);
$elevation = array(100,null,300,null);
$surface = array(null,null,3.24,null);
$timestr = pgstr($time);
$elevstr = pgstr($elevation);
$surfstr = pgstr($surface);
echo
"INSERT INTO sometable (name,time,elevation,surface) ".
"VALUES ('$name',unnest($timestr),unnest($elevstr),unnest($surfstr));";