put variable in sql statement php

This code is work if I change $table to  gel in line 12     how can I change $table to correct way

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$table = "gel";

echo "$table";

$sql ='INSERT INTO pong8_maintable ("timestamp8","Last","TradePrice", "TradeVolume" , "BestBid") 
SELECT 
cast(public.gel."Timestamp" as timestamp) ,

cast(public.$table. "Last" as numeric)  ,

cast(public.gel."Trade Price" as numeric)  ,  
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Error
pg_query(): Query failed: ERROR: syntax error at or near "$" LINE 8: cast(public.$table. "Last" as numeric) , ^
Error
Error while accessing the database:
ERROR: syntax error at or near "$" LINE 8: cast(public.$table. "Last" as numeric) ,
teeraAsked:
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skullnobrainsConnect With a Mentor Commented:
this works

$whatever = "foo $table bar";

this works as well

$whatever = 'foo '.$table.' bar';

this does not

$whatever = 'foo $table bar'; // substitution does not work inside single quotes

this is suited for user input and MySQL

$query = 'whatever = '.var_export($variable,true).' rest of query'; // and lets var_export handle the quoting if required

in postgres you additionally need to be careful with variable types. given the fact this is a table name use either of the 2 first samples. with the first, you need to backslash the existing double-quotes in the string or use single quotes instead.
0
 
Ray PaseurConnect With a Mentor Commented:
I think you may want to change your quote marks to allow variable substitution.
https://www.experts-exchange.com/articles/12241/Quotation-Marks-in-PHP.html
1
 
teeraAuthor Commented:
Thank you
0
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