The advance of large language models (LLMs) has unlocked great opportunities in complex multi-modal data management tasks, particularly in question answering (QA) over complicated multi-table relational data. Despite significant progress, systematically evaluating LLMs on multi-table QA remains a critical challenge due to the inherent complexity of analyzing the modality of relational data structures and the potentially large scale of serialized tabular data. Existing benchmarks primarily focus on single-table QA, failing to capture the intricacies of connections across multiple relational tables, as required in real-world domains such as finance, healthcare, and e-commerce. We present TQA-Bench, a long-context analytical multi-table QA benchmark derived from real-world public datasets, with a flexible sampling mechanism that varies context length (8K--64K tokens) and symbolic extensions for assessing reasoning beyond retrieval and pattern matching. We systematically evaluate a set of LLMs spanning model scales from 2 billion to 671 billion parameters. Our extensive experiments reveal critical insights into the performance of LLMs in multi-table QA, highlighting both challenges and opportunities for advancing their application in complex, data-driven environments.