I am building a PostgreSQL query through a script that returns formatted LaTeX formulas surrounded by double dollar signs, such as the following one:
$$6 x^{14} + \frac{7 x^{13}}{5} + \frac{13 x^{8}}{7} + \frac{5 x^{5}}{6}$$
Moreover, these formulas belong to an array, so that the complete INSERT query would be something like this:
INSERT INTO table("array")
VALUES (
'{"$$6 x^{14} + \frac{7 x^{13}}{5} + \frac{13 x^{8}}{7} + \frac{5 x^{5}}{6}$$",
"$$\frac{9 x^{11}}{13} + \frac{13 x^{9}}{7} + x^{8} + \frac{x^{6}}{3}$$",
"$$2 x^{13} + \frac{52 x^{12}}{3} + \frac{65 x^{4}}{9} + \frac{3}{2}$$"}'
)
However, following the INSERT, the backslash (\) that precedes frac disappears in the database (I get frac instead of \frac. Consequently my formulas do not render well in my application.
Here's the content of the cell:
{"$$6 x^{14} + frac{7 x^{13}}{5} + frac{13 x^{8}}{7} + frac{5 x^{5}}{6}$$",
"$$frac{9 x^{11}}{13} + frac{13 x^{9}}{7} + x^{8} + frac{x^{6}}{3}$$",
"$$2 x^{13} + frac{52 x^{12}}{3} + frac{65 x^{4}}{9} + frac{3}{2}$$"}
I use the sympy module in Python to automatically generate the formulas, so to manually double the backslashes before each frac is not an option.
What should I do to prevent this behavior from happening?
Backslash is an escape character in strings that represent an array of strings:
SELECT ('{a,"b\"c\\d"}'::text[])[2];
text
-------
b"c\d
(1 row)
If the backslash does not precede a character with a special meaning, it is ignored.
Double all the backslashes inside the string representation of a string array in PostgreSQL to get what you want.
If such backslashes are the only ones occurring in your string constant, you could proceed as follows:
SELECT replace(
'{"$$6 x^{14} + \frac{7 x^{13}}{5} + \frac{13 x^{8}}{7} + \frac{5 x^{5}}{6}$$",
"$$\frac{9 x^{11}}{13} + \frac{13 x^{9}}{7} + x^{8} + \frac{x^{6}}{3}$$",
"$$2 x^{13} + \frac{52 x^{12}}{3} + \frac{65 x^{4}}{9} + \frac{3}{2}$$"}',
'\',
'\\'
)::text[];