Almost every data vendor has a unique way of identifying companies in their database. When dealing with public companies, the ticker and/or CUSIP can also be downloaded. Tickers and CUSIPs are not unique to each data vendor and can be used to get data from different vendors. Below is a table of different vendors and often used company identifiers. For instance -the pricing database uses PERMNO & Compustat uses GVKEYS and they both can download tickers and CUSIPs. Tickers are unreliable as they can change and be reused so CUSIPs are the preferred identifier.
Below is a summary of identifiers and data vendors
Bloomberg -> CUSIP 9 digits & Ticker
Compustat -> CUSIP 9 digits & Ticker & can link to PERMNO & GVKEY
CRSP -> CUSIP 8 digits & Ticker & PERMNO & can link to GVKEY
Datastream -> modified CUSIP 9 digits & modified ticker & (for Tickers add U: for NYSE and AMEX and @ for Nasdaq and U: for 9 digit CUSIPs)
Execucomp -> CUSIP 8 digits & Ticker & can link to PERMNO & GVKEY
OptionMetrics -> CUSIP 8 digits & Ticker
SDC (mergers) -> CUSIP 6 digits & Ticker
SDC (Global new issues) -> CUSIP 9 digits & Ticker
To link to/from GVKEY and PERMNO, in WRDS use CRSP/Compustat merged.
More information on CUSIPs: