PostgreSQL交叉表，带有三列，值从一列汇总

I am new to SQL and was trying to do a crosstab in Postgres. I would have done it in Excel, but I have a database of around 3.5 million rows, 20,000 different values for code, 7 categories in cat, and variable values from 1 to 100. A code may only have few of the 7 categories. I am new to SQL and was trying to do a crosstab